I'm uber-happy with my P9 Covert. I think I have very close to 900 rounds of 124 Gr +P Gold Dots, 7 rounds of 127 +P+ Rangers and 20 rounds of CorBon 115 +P CorBons through her with not a single failure along with between 300 and 400 rounds of Winchester and S&B ball. Very nice gun, comfortable, reliable and very accurate for a small gun. Carries like nothing in one of two High Noon tuckable IWB holsters. It would be all but impossible to take mine away from me though I'd like to pick up a TP9.
I've shot several Kahrs including two different PM9s and have almost always been very impressed with them. I don't believe I've ever shot a small all-steel Kahr though.
As for barrel lengths, I'm not going to pocket-carry a Kahr as I have a KelTec for that purpose and if it's on my hip, I'd rather have a 3.5" or even a 4" barrel. It's only going to make it 1% more difficult to carry or conceal on the hip and I'd rather have the higher velocity. If I were wanting to primarily carry in the pocket, I'd probably go for the PM9.
If you already have a known reliable gun, if it's at all possible, I'd really try buy the PM9 and have both for a short time. If it is an even trade or something like that, I'd want to put at least 100 rounds of carry ammo through it before trading off my known-good gun for an unknown one.