[Rotting]

Putting a high-speed motor could chew up your gears, or even the pinion on your motor. First thing I'd do for more rate of fire is try getting a weaker spring. Sometimes the strength of your spring is too much for the current motor, and it needs to work harder to pull it back. With a weaker spring, your motor won't have to work as hard, and it can cycle it that much faster. Not to mention a weaker spring is also a good way to keep your FPS under any limits you want (staying under 350FPS with 0.20g usually isn't hard). On top of that, buying a weaker spring first to increase your ROF is quite a large chunk cheaper than buying a high speed motor. So I'd suggest a weaker spring first for ROF. If you're still not quite achieving the ROF you want, then you can go for the high-speed motor to achieve that. You'd have to find out roughly what the strength of your spring is, so you know what to replace it with. I'm sure someone knows what kind of spring comes stock with your M4. If you already have a pretty weak spring in your M4 stock from the manufacturer, then yea, just skip that step and try the motor.

Also, it's worth noting that high-speed can also be high-maintenance. I'm not well-familiar with high-speed, but most of the time high-speed requires more than just the motor. Usually need stronger gears, and I believe you also need a full-metal-teeth piston, otherwise it'll just shred your piston's teeth. Unfortunately high-speed isn't a 1-part modification. puts a fair amount of strain on your mechbox, and you should have the proper upgrades inside your mechbox to make sure it'll be able to handle high-speed.