My RWS 350 Magnum shoots 14.3 grain pellets at approx. 800 fps, but that's because I installed a JM seal in it, which is a bit tighter than the stock seal. Between the JM seal and the stock seal, I lose 13 fps with the JM, but I'm hoping the JM will settle in and give me better speeds after putting a few hundred rounds through it. Oh, don't forget I installed a Vortek Pro Guide 2 kit in my rifle, so I'm not getting spring torque or twang when I shoot; it's just a nice solid "thump."
My Gamo CFX with a JM seal and Theoben gas ram shoots 14.3 grain pellets approximately 650 fps. My other CFX with a JM seal and Nitro Piston gas ram actually shoots 30 (avg) fps slower. From 10 ft, they'll both sink lead into a 2x4, but they won't split the 2x4 like my RWS 350 did (stacked 5 pellets into it). I might have to order stock seals from Gamo for my CFXes and see what speeds I get with those.