Max it out.....if you do decide to shoot a mechanical make sure its a smaller one. I'd suggest less than 1 3/8" diameter. Snyper or a Rocket Steelhead would be good. The other thing to think about is if you're shooting a machanical head that's on the verge of being to large or is to large for your set-up.....you better think about your maximum shot distance. If your max is going to be 15 to 20 you're probably ok......if you have a maximum shot distance over 30 yards, be real careful.....longer shots really decrease your KE at impact.

Good Luck!