The PCV has much finer adjustments, meaning you can alter fuel at many RPMs. You can also remove fuel from certain areas if you want. The FMF just has 3 'zones' of adjustment and you can only add fuel. The PCV can also be used with the autotune, where it optimizes the air/fuel ratio under real use conditions.
As for peak HP, you can probably get about the same with either one. I have the FMF because it came on the bike when I bought it. I haven't splurged for the PCV because I don't know if it would be worth it for how I use the bike, plus my OCD would kick in and I would be constantly fiddling with it trying to get it just right.