RE: Which arrow is best for me for speed and accuracy???
To question 1: No, you have to subtract the weight of the insert, nock and vanes. Then divide that by arrow length.
You probably can still use the 5575's or 400 series with a 100 gr tip depending on bow. 5575's are around 8.1 gpi.
Speed does not reduce accuracy. I'm shooting at close to 300 fps just as accurately at when I had a old bow that shot 220 fps. However, a higher FOC will help accuracy and the faster the bow shoots the more tuning issues as well as shooting issues will be magnified.
I shot the XT hunters last year and they shot just fine. However, I cut off of both ends to try and get the arrows as straight as possible. They will shoot well, just not center punch with every arrow and one that is messed up bad will give you fits with a broadhead. If any are bent you can call GT and they will replace the bad ones.
Half inch doesn't matter as long as you are aiming at the vitals with a good shot. It could mean hitting the scapula or leg or missing vitals if you are off. The faster the bow the more you will appreciate straight arrows. The GT's could last you 2 or 3 years if you do not group shoot with them.