I know your question is dated Feb, but for the sake of a reply:
If you are talking about the high-flow valves for gas pistols/rifles, yes it gives a higher fps output, by how much? I am not familiar though.. However, the number of shots you will be able to make would be reduced as more gas will be used (we are talking about green gas right?). If you compare a stock valve vs a high-flow valve you will notice that the hole on the side is wider/bigger. hence, it is just a matter of modifying your stock valve (include the 0-rings).. Most likely by using your trusty rotary tool (dremel)...
You may also want to consider upgrading your barrel to a tighter one (6.00, 6.01mm) as this will also increase your fps.. A local guy in my location who mfrs barrels would usually say 20-30fps increase from his product but I also heard him before say that it was more like 50fps. I guess he was just giving a conservative figure to his clients. Effects of higher fps... Your plastic slide will NOT LAST LONG and better to upgrade to a metal slide...
To quote a local team here who specializes in pistol games (members buy pistols in pairs: eg TM hicapa 2pcs, TM Glock 2pcs per person) the best pistols in the market are from tokyo marui and Western arms... The first have fewer parts vs the second but both are highly reliable and durable...