Love my quadzilla race 0 60 100 140.
Have tried -
Edge EZ - Ran pretty good, but wanted more power. Towing egts were outa there set on the no longer availabe level 5 or 6 or whatever it was.
TS Ramifier - 100 hp, ran great, stong bottom end, fun box. I have one for sale in the classifieds.
Banks 6 gun with speed loader. JUNK! #@$%!
Like ASchwartz said, intake and exhaust need to be done first. I think its a good Idea to install gauges before anything so you can see what a difference each additional bomb makes. You can watch egts and boost and how fast or slow they rise, fall, and what they peak out at, as well as cruise. All good stuff to know. You really need em if you are going to tow with a box that isn't adjustable. That way, if you like to blast up hills with a trailer (I never do that

) you'll know when to ease off it a bit to keep from burnin her up. If you are interested in a single box, do a search on that box. There isn't too many products that improve power and efficency that don't get brought up eventually on this site. Good luck!
Oh, and BTW, from my expirences, some bombs may help MPG, some may not. The driver is the biggest variable. Good luck!