I shot 85 grain Montecs out of the Iron Mace last year - over 350 fps on the Speed Pro 5.5 shafts w/ gateway feathers.

They flew like darts, no problems.

I'd like to try the mechanicals, but I'm a little hesitant about the specter of them opening when I hit the trigger. Honestly, I don't know anyone else playing around at these speeds - and I'm not 100% convinced that the blades aren't flexing open when the arrow snaps out of the chute. I don't have a high speed camera to test it out... So...