The three SP's I have shot or owned that were rear-grip are:
MOA Maximum in 260 Rem. The MOA can only be configured in a rear grip. The 17 Mach IV was an orginal solid bottomed XP (dog-leg bolt handle) that had been fitted with a rear-grip stock. The third rear grip was a heavy barreled BAT action with a Jewel trigger and 18 inch barrel that was built specifically for 1k competition, chambered in 338 Lapua Improved. The 17 wasn't braked but the other two barrels are. The reason I mentioned them as rear grips is that MY XP's are all center-grips. A center grip is easier in that the ocular is closer to you than with a rear grip. It is a different feel to shoot a high mag rifle scope on a handgun and in my opintion it is easirer with a center-grip, but you can do it with a rear grip like a MOA or a Contender/Encore. I would get whatever rifle scoe that you already own and play around with it and the best way it works for you. Get up close and get your full field of view then back off far enough to MAKE SURE you don't get kissed. Weight of SP, cartridge, and whether or not it is braked will determine how far you need to be away from it. Leupold has one of the longest ER's in the high mag scopes. Sightron makes a 24x that has LER for a rifle but it's relief picture falls off quickly as you move back whereas Leupold is a gradual reduction in sight picture.
I'm going to shoot this May in a specialty handgun seminar and one of the rigs I will use for doing primarily all field shooting @ unknown ranges from field positions at steel targets the size of big games vitals out to about 500 yards will be a XP-100 with a 6-24 Burris Black Diamond with the Ballistic Mil-Dot reticle. I have put several 100 rounds through this XP already with other rifle scopes, but this will primarily be field positions. XP is chambered in 284 Winchester.