i went from the 'D' valve to the Forge DV - Yellow Spring - it was part of my quest to solve a flat spot - turned out to be the revo settings in the end
i also changed as I heard the noise was a bit fruitier with the forge - which it is when paired with a CAI in particular the ITG.
in terms of performance - forge seems to work well and holds boost solidly but so did the 'd' valve - there is a huge thread over on golfmkv.com comparing the two with logs etc - which shows the D valve works just as well
i like forge stuff though - uk company and their products seem well developed and produced, aftercare is always good too