I can help you with my experience maybe. I bought the M16 advanced version of Buyairsoft.ca, and it was supposely shooting 375fps. When testing it, it shot 330 with .2g, all I did is change the spring, it now shoots pretty consistensly around 393fps, considering the 509mm Tighbore barrel included in it, it's the same feeling than my previous G3-SG1 with upgrades. I've got told by the seller that the silver electroplated tightbore is the same for both version.
Overall, I love this gun, all I was hoping is that it would be as good as my TM G3 was, and it's actually doing very good!