Agreed with what Big Jim says. I use GT 1535's on my 48 lbs bows. I leave them uncut and use a standard GT insert and nock which are both around the 12 grains. I use a 100 grains front load. Bows are center cut. They give me a perfect flight. At a draw weight of 48 lbs I end up with 8,5 gpp, which is ok for me. Cutting the shaft and using higher frontloads will increase your gpp's if that's what you want. Last time I trained on a 60 yards distance and I could easily hit a balloon with that set up.
As for tuning, you can play with building out your strikeplate, (when your bow is cut pas center) try some different weight field points, or cut the length. GT also has weight adaptors which you can screw into the standard inserts even when they are glued in. But you need a special tool for that.
I like the GT traditionals 1535 that much, I have a stock of 72 pcs. Big Jim Blems, that is
They became pretty much my standard shafts for my 45 to 48 lbs bows. That Big Jim glues the inserts in for no extra costs, is a great service, and I never had a insert coming loose till now...