Ok........at 58 lbs. you probably should stay with a fixed head.A 3 blade Muzzy or Thunderhead would be good. I think they have a 1 3/16" cut. There's lots of good fixed heads. If you increased to 65 lbs. you need to find out more about your bows performance. You can probably get by with a medium size mechanical head like a 1 3/8" diameter. If you find out your KE is over 60 you could go with a bigger 1 1/2" to 1 3/4" mecanical.

Good Luck