I've shot both the 5575 and the7595 with 100 thunderheads out of my 70# hoyt. The 5575 hits 2-3" right of the other. Haven't put an 85grn. head on yet, but believe it will bring it closer to the other (there's no difference with FP's). Your not tuned or your not a good enough shooter to determine it. I think your just not tuned yet and a 125 is too heavy unless your using a 5" vane. With that heavy head your causing the 5575 shaft to flex a great dealto get that head going, a 7595 would work better with a 125 head, it's stiffer. Adding weight to the rear end will offset the effect.I shoot the 7595, but my bow is 70#. If a 5575 won't do a 60# bow GT's got some problems.

Shouldn't be that far off of FP's, (2" max at 40 yrds.)but IMO I see no reason they have to shoot the same as a FP as long as they hit what I'm aiming at.

FWIW Once you get it shooting well and your sure of it, don't stop there.Trying changing things one at a time and you'll know for future ref. the effect things have.