First, the basic frames are identical, only the grip frames, hammers and barrel lengths available differ. Back before the "New Model" series, the SBH and Blackhawk primary frames were different, that's no longer the situation.
If you want a really long barrel, you have to go SBH. Unless you want a totally custom barrel done up, which can be done on any of 'em.
The square-rear triggerguard on most SBHs is sometimes a problem (it can whack some people's knuckles under heavy recoil) but that can be solved by grips that fill in the space between the trigger guard and grip frame. Or change the entire grip frame out to some other style - Qualite has brass or stainless grip frames similar to a standard Blackhawk/Vaquero, or they and several others sell bird's-head grips popular with those with small hands.
The Bisley/Vaquero Bisley-type grip frame has a reputation for absorbing big recoil the best. And since the Bisley family guns place the hammer lower, if you must have an adjustable-rear-sight SA Ruger, the Bisley hammer will place your thumb furthest from the rear sight, reducing the odds you'll "hang up" on the rear sight.
Caliber: there's a lot of good info coming out now showing that the .45LC has major advantages over .44Mag. Because the case volume is greater for the .45LC, you can get .44Mag power levels or beyond with LESS peak chamber pressure, leading to greater accuracy and less recoil. True, the ammo choices aren't as broad as .44Mag but Cor-Bon has good JSP and JHP .45LP+P deer loads that rival the .44Mag, and Buffalo Bore has a really slick 325grain hardcast doing over 1,300fps that leaves almost all factory .44Mag fodder for dead. Or you can handload; recipes for hot .45LC+P that work specifically in tough Rugers are widely published online and in print. John Linebaugh has done the most research on wildchild .45LCs, goto
http://www.sixgunner.com and follow the link to the Linebaugh page from there. Read what Linebaugh has to say on .45LC versus .44Mag, and you won't want a .44Mag. He includes load data - a lot of it.
What else...there are UNcataloged runs of stainless convertable .45LC/45ACP guns. Most are Vaqueros. A distributor called Davidsons did most of 'em - goto
www.gunbroker.com or
www.auctionarms.com and search under either "Blackhawk" or "Vaquero" plus the term "convertable". Another really weird combo is the .38-40 and .40S&W convertables, and the .40S&W cylinder can easily be reamed by just about any gunsmith to 10mm or even 10mm Magnum
.