1) What do you own?
6" blued and 4" stainless
2) What grips do you use?
stock hogue monogrips
3) What loads do you use?
for range fun - Amer. Eagle or Winchester white box 130gr FMJ .38spl, and whatever .357 I can find cheap (currently a couple of boxes of Remington 125gr semi-jacketed softpoint). For home defense in the 4" - winchester silvertip 125gr .38spl+P. I'll probably not buy any .357 loads less then 145gr again, as I've since seen the kind of flame cutting those 125gr .357's can do with time (on someone else's Smith 686).
5) What would you like Ruger to do differently to a GP100?
Bring back the half lug varients as they do offer a noticably different feel to the balance, especially in the 6". Also go to a higher viz front sight.
6) Holster(s)?
At home, my 4" sits in an inexpensive Uncle Mike's sidekick. Otherwise, mine have their own nice Ruger-branded pistol rugs (the new ones, with the intercept rust inhibitor lining).
7) Speed Loader(s)?
Don't use 'em. At home I keep 12 reloads in a leather cartridge slide velcroed onto the Uncle Mike's.
Some not-so-great pics:
My Rugers:
First 12 rounds out of my 4" - factory new right out of the box, 130gr FMJ .38spl, shot two handed, standing, SA, 25 yards outdoor range (home printed target on 8.5x11 paper):