No "Stock" baseline... but here's the comparison going from the cat-back, to the headers, to the tune:
2011 LS3 w K&N, Magnaflow Comp Cat Back:
W/ SW 1 7/8" LT Headers NO tune:
Completed, WITH tune:
Not too shabby, especially at 95 degrees and 90% humidity!
Need to come up with another 22 HP and I'll be happy!