I've had mine for about 15 months and it's doing great. It's favored pellets are JSB Schaks 4.5mm/8.2gr @ 545fps. It will hit higher velocities with lighter pellets, but accuracy is sacrificed for the extra speed so I stick with what it likes accuracy wise.
Mine seemed to take a while to break-in, probably around 1000rds. I do believe that a large part of it though was learning the pistol and figuring out the best hold and doing it consistently.
I sort of home tuned mine, I realized that the spring guide could be solid since there is no piston rod to deal with. So I filled the guide with epoxy, taking away some of the noise of the shot cycle, and at the same time the epoxy caused the guide to swell slightly giving it a tighter fit in the mainspring which elimiated any buzz or twang.
Over all I'm very pleased with the power and accuracy of the P5. I hope you enjoy yours!