Honestly, any upgrade you do will promote faster wear on stock components.
I have skirmished my MP7 in the following manner:
Bone stock - Using 9.6v 1700mah (*not recommended*). 2 Games, ~3000rnds
Fully Modified - Using 8.4v 1200mah mini (*ok to use*) +10 Games, ~15,000+ rnds
I've opened up the gearbox about 4 times and the gears have shown no significant wear n tear from the higher voltage and mah batteries.
I guess it all depends on maintanence and how u lube and install your parts.