Just a note: tank to tank comparisons aren't the best way to judge the effectiveness of mods. For the vast majority of drivers, there's just too much normal variation to be able to say with any certainty if a mod has helped, hurt, or done nothing at all.
See:
http://ecomodder.com/forum/showthrea...ery-11445.html
For simplicity's sake, you could tease out a simple "better/worse/no change" result in an hour or so with coast-down, or terminal velocity downhill testing.