Tru Flites test said as close to eight as you can get. Spin does indeed equal stability. Theve been doing what the do for many years with great success, so thats who I trust. Eight does get noisy, especially with feathers but since feathers grab more air and stabilize quicker, you dont need that much with feathers. True Flites test was geared towards vanes.I use an Arizona ez flex pro or alluminum model at six degrees heli, which was originally 8 degrees heli that I heated and twisted and also another one that was one degree offset that I heated in the oven, twisted and made five degree offset. The alluminum model will work on carbons if your really carefull and prepare the shaft.Arizona also makes their carbon model in 6 which would have saved a hell of a lot of time, but I got the others at a sale for next to nothing so worked with what I had. Its taken some doing over time but b.hds. should always hit very close to f.pts. If they dont you may have a tuned bow, but you dont have arrows tuned precisely to the bow. Using perfect form while paper tuning you can get acceptable tears with a horribly over or underspined arrow but bare shafting and b.h. tuning will tell the truth very quickly.If you can get within a couple inches at 40, thats pretty good but there is absolutely no reason why b.hds. shouldnt hit with f.pts. even at 300 f.p.s. It just takes time, energy, and experimentation with finding the proper arrow spine,vane lenght, f.o.c., arrow length, etc. Thats one of the main reasons, when I find a bow arrow combo that works for me, Ill shoot it till theres nothing left and then find a bow with specs close or equal to what I had. I couldnt do what PA Bowhunter does. If I got a new bow every 6 months and had to worry about all that tuning, Id be a quivering mass of worthless flesh.Finding the proper setup is usually a long drawn out process. Getting close and just moving your sight pins for b.hds. will of course work, but you can still go farther.