Ill def have a look at the software most software ive used is for 2D I have to jump,,, My original intention was to build a machine 2 metres x 1 metre with a 200 Z but found my budget is better than I thought so Bigger it goes,,There are various long V cutting bits for granite now on the Market But a decent 3KW spindle will cut through anything as long as the feed rate is correct Gooing to 4.5 KW or higher doesn't make much difference these are usually to drive Long bits or large blades.. Diamond has a finite working speed if too high it burnishes the Bits exactly the same as Using Carbide bits on granite and polishes the diamond flat.. the only machines ive seen belt driven are small 2D cutters.