Blacksmoke,
Great groups!
Martin,
I had a few fast twist bbls that would run full throttle loads but the majority of them tended to be fairly limited on how much horsepower you can put on a PRB without giving up accuracy. Yes, we all know, myself included, that running hotrod loads isn't "necessary" but it sure is fun annoying the suppository gun shooters on the range and I do like having a buffer zone when hunting. For a dedicated paper puncher though, running light loads is much more enjoyable and economical which is why I swing both ways on this issue.
The 12" .36 1:48 wanted a 0.355" ball wrapped in a 0.012" patch and 28gr of 3F; it just refused to print if anything was changed. On the flip side, I have seen some faster twist bores that aren't picky at all and will let you push a PRB as fast you like but in my experience they tend to be the exceptions.
Underhammer buggy rifles are slick but it depends on what you're doing with it as to what would be the most appropriate choice in rifling and bore size. For a hunting application, the choice of gun likely means you'll be using it in thick cover where I myself would opt for a .58, .62 or .66 bore with slow twist for the simple fact of combining horsepower and momentum. Tight shooting is fast and a scrub, sapling, vine or palmetto stalk isn't readily seen when you have a tusker running up on you and since I can't run or climb anymore, I much prefer having a bigger ball with more than enough velocity on it. On the same note, that's not something I'd like to spend a day punching paper or tree rats with either.
I don't pass judgment on anything, just stating that in my experience, slower twist bores have consistently offered more PRB loading options than bores with faster twists. I have a couple customers running match rifles with 1:72 twist .40's and a varmint hunter running a 1:30 twist .40 so my opinion remains that as long as shooter is happy, that's all that really matters.