Thank you all....
I don't want to bug the Proof guys until I have the $$ and am ready to do a possible build. As a business owner, I know how much enormous amount of time I waste with tire-kickers, and don't wish to do that to others trying to make a living until I'm serious about buying. You guys, OTOH - I will gladly waste your time.
The Proof/ABS method & materials of CF-wrapping is known to be superior to the Christensen method (for the same or less $$, to boot). The dual/interlaced CF-based materials dissipates heat better. Christensens are ok, but Proof definitely better, say many in the know. See, e.g., SnipersHide, 24HourCampfire, LongRangeHunting, etc.
This is the ultimate just one build, if I do it. It *MUST* have the long bbl to squeeze every bit of performance out of a non-overbore round like .260, and how do you think a 27" pencil barrel will perform (and look)? I don't know for sure (not ruling it out), but I don't think very well. So for the same weight (or just almost), I can have a stiff & long bbl, using CF-wrapping.
Cost isn't an issue on an "ultimate build", by my definition. The whole point of an ultimate build is "without regard to cost; with regard solely to performance, etc.". However, lighter IS better. So I'm taking what you're saying to heart (taylorce1). If I can truly get a non-CF bbl that is both lighter and equally accurate in the 27" range, then I'm all about that instead, without a doubt. I just need some real numbers and more input / experience. I could be convinced to go as short as 26" or as long as 29", potentially, but I think 27" is where it's at for this build, give or take 1/2".
There is no doubt in my mind that I could build a 20 or 22" rifle with: equal accuracy (cold bbl), lighter weight, and more external ballistic performance, from a pencil hunting barrel in .26 Nosler or similar in a long or magnum action. But I do NOT want such a rifle. I don't want a barrel burner, and I want a short action. If I'm gonna plunk down that much for a barrel, it needs to last a looong time, and retain re-sale value, which non-barrel burners do. The chambering is decided now - .260 rem. As is the approx. bbl length. I will consider if you still have a cogent reason why I should budge from these, but I'm starting to get fairly well set on those two decisions. So keep the input coming if I'm just all wet here.
If it helps, the two hunting scenarios for this rifle are (1) Plains & desert speed goats & mulies; and (2) High-alpine (mostly above treeline) steep & mountainous sheep, goats, ibex, etc. So both are open-ish, where the long bbl won't hamper me. Shots will ALWAYS be rested - never a snapshot. I need lightest weight with very good long-range performance. I want to have a PBR of 300+ and I want to be able to *confidently* & consistently shoot well at 400 (or maybe 425 or 450 even), using Kentucky doping. This rifle is NOT for general woodsy or mixed-terrain low- and mid-altitude hunting, and not for larger game, elk+. I have other rifles for that. Just wide-open plains/desert, AND mostly-above-treeline.
But also, for spits and giggles, I want this rifle so accurate at 600+ that I could hang in toward the bottom of an F class match and/or practical shoot... not win or place high, but *with appropriately-developed skill & ammo* mind you, just hang in without a DQ or lowest score ever obtained in the history of those comps by a mile. I'm OK with lowest score ever obtained, just not "by a mile".
So I want the heat dissipation & stringing-resistance that a pencil-bbl won't give me. The bonus is not having to spend all day at the range for load development, waiting for it to cool between shots. See what I'm after here?
In truth, if I build this, it will replace two current rifles: an ultralight in .280 rem with 22.25" bbl (the high alpine rifle), and a heavy custom in .280 AI with a 23.5" bbl (the plains/desert rifle). I want the external ballistic performance of the 2nd one, with the weight of the first one, you see? My thinking is that a 129 Nosler Accubond LR from a 27" bbl in .260 rem will have the same or better external ballistics as the 154 Hornady Interbond from a 23.5" .280 AI (but lighter rifle - so I get my plains / desert rifle in a lighter config), AND have much better external ballistics than the 139 Interbond in .280 rem from 22.25" (but roughly same weight - so I get my high alpine rifle with both better ballistics and less recoil).
And the new rifle would have same or better accuracy than either, I hope, espec. when hot. And could even be potentially used in competition - it will easily make weight, lol.
And the best part is that this allows simplification by replacing two rifles with one - If Gordon Gecko were a hunter with an actual life, too, he would say "Simple ... is GOOOD!"
Simplification might very well make $5 or $6K for such a build worth it.
(Coincidentally, if you're curious, it definitely WILL make it "worth it" if Proof or similar can make my stock I want, which no one has ever made before commercially, with their Lone Wolf or a Manners as a starting point. I have made the stock I want myself, but it took an inordinate amount of time & frustration with my lack of skill and tools. So I don't want to go through that again, and the stock I built won't fit a Rem 700 footprint. It fits a Wby Mk V and isn't overly-aesthetically-pleasing, to put it mildly, lol. Now if Proof or similar will not or cannot, for whatever reason, build the stock I want along with the rest of these requirements I want, then I certainly will not be doing this. But I haven't inquired yet, so I don't know. PM me if you want more info on this).
Taylorce1, do you know - Who makes a commercial custom action which is as light as, or lighter, than the Rem 700 Ti? I need to know whether I need to be scanning for used SA Ti rifles, or not. (Either Rem 700 or Browning A-Bolt perhaps?). Does anyone make a custom Ti action? Or will Proof require that I use the Defiance Rebel? I need to know some weights... Are you saying that the Rem 700 Ti is 2 oz lighter than the lightest one you know of with that footprint? I'm not sure 2 oz is enough to worry about. 4 oz would be, but not 2, I don't think. Oh, and having it come in under 7 lbs or right at 7.0 lbs bare is ok, I've decided, based on your input. I'd much prefer 6.5 or less, obviously, and I will not do it if it's even 7.1 bare (I will come off of 27" down to 26 or less if need be to obtain 7.0 or less). Gotta draw the line somewhere and it may as well be at 7.0. BUT - if the two oz. save from a Rem 700 Ti is the difference between 7.1 and 6.9 bare and still keep the 27" bbl, then that just may be the thing I have to do then!
P.S. I suspect that the scope for this rifle will be the Accupoint 3-9x40mm, but I'm still open to ideas. Possibly the Accupoint 5-20x50. I wish there was an Accupoint in 4-16x44 or similar - that would be the shiznizzle for this build.