Tommorow i'm going to order my dad Bowtech Tomkat package off of huntersfriend. I think i have everything right except for theshaft sizeof the Easton ST Axis arrows i'm going to get him. He's going to be pulling back 55 pounds with a 28 1/2 draw length. So what do you think i should get, theshaft size options are 500, 400, 340 and 300.

I would try the 400 spine myself.

Yep. 400's are perfect. While at the arrow length you'll be getting, you could most likely get by w/ the 500, best to be slightly overspined than right on the line or underspined.