Your draw length and your draw weight AND you tip weight determine what spine arrow you need. All 3 together must be considered. A heavier tip will make an arrow flex more as will a longer draw length. If you plan on hunting anything heavier than deer I would suggest a 125 gr or heavier head. The amount of speed loss will be negligable compared to the better penetration. Your archery shop should be able to set you up properly.
Halfbaked - did you read your pm I sent you a few days ago?