My advice, if you want it to last long at that velocity...
Lonex A1 motor
11.1v lipo battery (could get away with a 15C discharge rate)
M140/M150 spring
Upgraded cylinder head with 70oo sorbo buddies installed
Lonex Red piston
Upgraded metal nozzle with o-ring
Buy the above here:
http://www.airsoftstore.ca
Also from my experience, the Systema "reinforced" gearboxes aren't terribly strong, so radius the cylinder windows for increased durability.