I thought about counter weights but I think in the long run it'll be better to change up the lead screw.

I am now wondering (after I just ordered one), can I run two different screws with Mach 3?

Meaning, X and Y will run on 1/2 5 start acme screw. Z will be on a 16mm x 5mm pitch screw.

From Amazon...
300mm/11.81 inch Ball Screw RM/SFU1605 (Diameter 16mm, Pitch 5mm) with Metal Ball Screw Nut and BK/BF End Supports for DIY CNC Machine and 3D Printer