I have the 67mm. And it is a pretty good improvement in throttle response, but it is also something you will have to get used to and I have heard of some people that didn't like it. In terms of power you will not get any noticeable improvement. 67mm or 65mm wont make any difference. In my opinion this was one of the worst mods I did to my car not because I don't like how it drives, just because for $250 u can get better mods. On your question which would be better to get, I would say if they are the same price I would go with the 67mm, cant hurt. But if you can get the 65mm for just 5 bucks cheaper I'd go with that since there wont be any difference in performance.
The 65mm is an older design, that's all. Focus Central used to make them. When FC went under, CFM bought up a lot of their stock and resold them under their name. CFM eventually began making their own improved design: the 67mm. It addressed a number of driveability issues the old FC units had; and while the opening is 2mm larger, the naming is largely just to differentiate between the two designs.
Also, there is a definite improvement with a 67mm in throttle response. The SVT has pretty bad response in stock form; I can press the gas and let go of it before the revs even start to go up. With the 67mm the response is so much better. And YES, this will require you to re-learn your driving habits with the car. It is a lot different if you're used to driving around with stock throttle response, and like opyaFSVT said, I wasn't sure I liked it at first. Within a couple days though, I just loved it... the car went when I wanted it to.
i like my CFM 67mm TB. a somewhat of a very little quick response, can feel the small gain after 5k rpm to redline. and i like the whirlin/whistlin noise it has to it. kinda like a supercharger but it not one!
I agree with CaysE. I think you posted in my last thread about the CFM 67mm TB. I have had it on not even a week, and the throttle response is noticeable. Not really worth $250, but whenever I punch it, the car goes. Get ready to learn how to redrive the car though. Very different feel.
i already portd the stock one, at 1st i wasnt gonna go to fi but my clutch my be starting to go and if i have to go through the trouble of doing that i may just go to a turbo with a clutch so idk what im gonna do