I only use pistols, they teach you how to move and conserve your ammo. Also the transition to aeg is much better since you are shooting what you see, not just full auto everything. It only takes one bb to get someone out. there is a good website dedicated to pistols only, google the POR, pistol only revolution, it's a good read.
I've had the mk23 and it's great, silent and conserves gas. Only thing to remember with nbb is that each trigger pull puts the next bb in, so 1 on 1 is ok but 2 or more is not a good idea. The TM mk23 is a different playing style IMO, it's more stealthy and you pick your shots off.
I would suggest any hi capa from TM, they are amazing stock and get even better with the right upgrades. I would choose my stock 5.1 to my old upgraded ksc g17 any day. Also owned a TM de, TM 1911 meu, and ksc g19. hi capas and meu's all the way!!