Have you dealt with AEG's before? Because 500 fps is hard to do. Alot of things can go wrong in set ups like these. You will need a MOSFET, 11.1v lipo, high torque motor, 300% gears (if you aren't super worried about TR), and GREAT shimming. Then yeah, a nice piston, and the AoE needs to be perfect. You will also need a really tough GB shell, and sorbothane padding so you don't get a fracture. A ton of tuning needs to be done, and V2 GB's are harder to work with. I would recommend you get comfortable with GB's before you go all out on a DMR build. Also, note that those upgrades were just for durability, but DMR's need more parts. You can't just drop in and go, you definitely need to tune, and tune, and tune.