For what its worth,
Made some runs after splitting my stock pipe system. One side is stock with a Flowmaster and one side is straight piped. I also added a SD Lift Pump since my last trip to the track.
Hard to say which may have helped, but I improved my best ET by a 0.07 (8.28 ET) during a Local diesel GTG. I only ran out a few of the runs so, I may have gained more than a 0.07. I was on an 8.25 run according to the 330ft ET once, but got out of it during eliminations. I think the air was bad as many of the guys sad they were running off their times a little. I was expecting more.

The GTG race was fun though and I made it to the final run only to turn my best time with an 8.28 on a 8.34 dial in. yep, caught that did ya, "Mr. hammer down" had to catch up to my opponents 9.10 dial in. I went by him alright.............:rolleyes:

For the record I was able to move my Edge box up only one level from 2 to 3 (Quad is always on 215 hp level) without bursting. I tried level 5 and "she" started bucking like crazy before the 330ft mark. :mad:

Between a flowmaster and a straight pipe I don't think you would see much difference as your results lean towards. However, like you said weather conditions changed plus you added a lift pump. Too many variables. I am still running stock exhaust and muff. but am planning on changing it also. I will be doing that in Jersey so I will have to get some new baselines there before doing the work.

Thanks for the report on the lift pump. I was looking into one because I can only run the Quad215/HotJuice-4. If I go 5 on the juice I surge like madd!! I think I'll hold off for a little while, it runs good enough for now......;) Yea Right!!:D

If I were adding exhaust again, I would keep the stock muffler and simply straight pipe (no muffler) the other side as I have done. I furnished the cutout from Jegs and the muffler shop did the work for $200. Cheap enough for me and I can close the cutout with a block plate if I wanted to. The new exhaust exits on the drivers side (matches) as the stock exhaust does on the passenger side.
It's cheap and works.
However, the Flowmaster muffler does sound good (it's been on there over a year), and the new straight piped side is a little louder.