I shoot and 8" J&J brass barrel on my mag most of the time. I have barrels from 8" to 16" and the 8 shoots as good as any. The only thing I really notice is the change in sound signature.
I think if you have a good bore/paint match barrels length has very little to no affect on performance. I think more is gained with a longer barrel strictly with stability and "site plane" more than actual performance from the barrel.