Just for a comparison of loads in different ranges look through this, if you haven't already,
Brian Pearce .45 Colt 45-270-SAA
When you consider that the loads listed here cover such a wide aspect of the different revolvers out there today, you can easily get by without working up into the higher octane loads.
I am shooting a Redhawk which if the past 30yrs or so with the other two in 41 and 44 magnum, are any indication of how well they handle upper limit loads, I could really stretch the 45 Colt out. That said I have found that I or most who shoot the Colt have no real reason to load to the higher pressures unless it is for hunting big nasty things that will hunt you back. You will find that even with the modest loads running 1000fps or less, these big chunks of lead will just plow right on through most things with not, much if any, reservation.
I have one of the MP molds in the 45-270 SAA version and must say that it is plenty for anything I would eve need to put it through. I know your looking into the 300gr loads, but in my testing they simply haven't done anything I couldn't do with the slightly lighter bullets a bit more accurately. To be honest my most accurate load is the Lee 452-255RF loaded over around 8-9grs of Unique. These run just under 1000fps out of my 7.5" barrel and will usually shoot very close to a 1" ragged hole if I am on my game.
I did suggest the Ruger convertible, as to me for an entry level revolver for someone who is running things on a tight budget already, it is simply getting two revolvers for the price of one. On the one hand you have the cheaper ACP which even if you don't reload you can still find fairly cheap ammo to practice with and at least end up with your own once fired brass. Even if you went the full reloading route you can find once fired ACP for sale in a lot of the forums a whole lot cheaper than the Colt brass. As for loads, you can also use a LOT of 45 cal bullets with the revolver that might play hell with the auto version. Like I mentioned before, it is pretty easy to run the 255gr bullets out of the ACP cases using the revolver and still stay within ACP pressures.
The flip side to that is the Colt cylinder. You can pick up 500 Starline cases and be for the most part set for life if your sticking with standard loads and not crimping the daylights out of them. Those medium to heavy .452 bullets as mentioned above will still rock even at the standard velocities.
For a long time I was an impulse shopper in that I would jump into things without much regard to what everything else had to offer. I purchased the latest greatest fishing reels when I was fishing tournaments that were faster smoother and yada yada. With my rifles well I wanted similar criteria, and didn't look to see that something only a little different could offer me a lot more in the long run. Now I look to see not only what it can do for the intended purpose, but what else I can incorporate into it. Now my fishing reels are the old Garcia's which will handle most any fish the line can handle and they are tough as nails, like the Rugers. Not pretty or fancy but will work a lifetime, and are built like tanks. Most every rifle I have is off the '06 or 308 case. I can use the same brass for nearly all of them in which ever size is needed. So I get more bang for my buck when I purchased the standard cases in bulk, even i I don't size them up, down, or blow them out to different calibers.
Like I mentioned, I am looking for the BH Convertible for the wife. The smaller grips and lighter weight will allow her to shoot with me, and be comfortable while doing so with the ACP cylinder. Not that she is recoil shy, but she is only 5'1", and those RH's are a bit much for her stretched out at arms length. The recoil isn't an issue as she learned to shoot revolvers with top end loads through my then scoped 44 from a rest. The first day she shot her new GP-100, she stood up after loading it, and rolled six rounds into the 3" bull at 25yds. She likes to shoot, just not with the heavy weight revolvers I like. With the BH, she will be able to come out and shoot with me, and when she doesn't I will swap out the cylinders and go have fun on my own. Oh and it will also be a bit part of my grandson's learning to shoot revolvers as well. So the advantages are there, I just have to find the one I am looking for when I have the cash to pick it up.
Hope this helps,
So not considering the 300gr weights, which some folks find they cannot live without, I haven't really seen the need for them in the Colt. The wide variety of styles in lesser weight bullets has had me plenty happy. There really is something magical about an old SWC sticking up outta one of those fat cases that just does something for me.