Not sure of the work Tom has done on the MTX-75... I know he is the Tuning guy around here. The MTX-75 is from what I have seen a better transmission as there is more aftermarket support for flywheels, clutches, differentials, and gears.
The CAT back is the same regardless of SVT or ZX3 or standard Zetec equipped Focus... so if you get a cat back and then eventually get a SVT header you don't have to change it. you will only need a SVT header, CAT, and Flex Pipe. The thing is I think you will get more performance gain from spending the $$ on a CAT back then on a shorty header that leaves your stock CAT.
I am not sure on the prices, I have not done anything with the SVT suspension for years.
Not sure where you got the hood scoop from or are you just making that as a statement... I have only had the Iceman so can't compare it to the K&N gen 2. I can say that I think the Amsoil Dry filter is better than the K&N oiled filter. but yet again I have not had the Amsoil either to directly compare. the nice thing about the FocusSport (now FSWerks) air intake is that it has a good heat shield on it. Leave the air ducting that routes from the front bumper to the stock air box as it will bring cooler air still by the bumper.
2001 ZX3 2.0L Zetec-
Hatch Nation #42
Going through Rebuild See "The TICK Build Thread" for details (http://www.focusfanatics.com/forum/showthread.php?t=289168&referrerid=62897)