As regard suitability for rats, i have routinely taken them with this pistol. It has been specially tuned to produce a damped 520 fps with 8 grain Domes. 500 fps is a realistic figure provided you can group tight and restrict the range. The above group has been deliberately shot with 2 clicks low of point of aim to show accuracy at my usual 8 to 12 paces. Aiming just behind the eye, i have found the pellet will often shoot clean through.
I prefer a Dome pellet like an AA express or Falcon because they retain almost all their energy at these ranges. Taken together, i feel this is a realistic proposition for such shooting.
People will often attack shooters that choose a pistol for such shooting but will usually lack the required pistol marksmanship.
Practise and discipline is required for sure, but 500 fps is enough. I have found that a Domed pellet from my rig above, will retain approx 480 fps at point of impact across the first 12 yards and will cleanly penetrate both sides of a household tin can, or approx 8 beer tinnies. I tend to set an absolute max range of 15 yards, after which accuracy and velocity starts to drop off rapidly.