I run them; have not noticed any difference, but they SHOULD (1) ad a pony or two as mentioned, and (2) help reduce (just a tad) engine heat (less friction).  The butt dyno, though, has not picked out any differences...  I guess it's a good addition to all the other mods (ignition, high flow filter, cat and cat back, more aggressive cam, 62mm TB, eFan, etc.).  Not sure if I would buy them again, though.