ORIGINAL: anuthabubba
You might want to consider a Magic Muffler type mini-pipe such as the JettStream, MVVS 3253, UltraThrust or even a home made mousse-can type. These offer a broader range of rpm boost along with better throttling response. Some report as much as 1,400 RPM boost (in high RPM engine setups) with these types of exhausts. You would surely get several hundred more rpm.
The nice things about the MVVS item, are its relative low cost and the fact that the header will fit unaltered onto the Fox's exhaust stack.