Re: straight pipe, x pipe or H pipe?
I have been doing H's on mine and customers since the 80's. It does seem to help low end, and it certainly makes the exhaust sound better, less "blat" with loud exhaust and more growl.
As far as X versus H, my number one determiner is how well either fits. An X on my Mustang would have to hang too low, so I used a 3 inch exhaust with a 3 inch H.
On my F100, I am going to run 3 inch, with a 3 inch X, I don't expect any significant difference over an H, but it fits and has cool points.
My opinion X or H isn't as critical, but either is important over unbalanced straight pipe.
70 Sportsroof, 427 FE/489 cid, TKO-600, 31 spline 4.10, A/C. modified Mass-flo EFI/reprogrammed A9L/CnC ported Victor.