The version numbers are to do with Barrel length of your gun and not FPS. It's just a guide to make sure you are not buying something that will be over/underpowered for you barrel length.
It's a bit confusing as some websites have the extra info and a lot dont. If you go to G&P's main webiste:
ONLY For Marui M4A1 MWS GBB
Including 90° piston cup O-ring to prevent leak out the gas
Suggest using below 263mm inner barrel
134A only
http://www.gp-web.com/product/mws037a/
so If you are running a stock barrel you'd be looking for that one. I have a 370mm Barrel and run the 4.5 (gold) version.
The valve gives you the ability to tune your FPS based on BB weight, barrel length, type of gas and temperature.