Squirrels and rabbits I just use a little HW50S. Its only 12ftlbs but I've taken squirrel as far as 55yds with that. Very accurate gun and very well made for not much more than what a 135 goes for. You really don't need all that power and it just takes away from accuracy unless you really know what you're doing. Even then, good luck.
For groundhogs I usually use my HW97K that's tuned to 17fpe. Thats a short range gun for them though. If I can't get within 30yds I dont take the shot on account of the lower power. Damn accurate gun though. I've taken squirrels at 70yds with that one.
If you plan on going bigger than groundhogs or game similar to that size more often than not, I would stick to PCP. Easier to shoot and quite a bit more oomph.