I have modded my heq5 pro, so i can give some feedback as to how they perform. The main thing you will notice when you use it will be the rattle of the gears meshing is gone. The performance of the mount will be around the same but backlash is essentially eliminated, this has a large positive impact on pointing. Guiding is essentially the same I could not comment much on guiding or PE.
One thing about the belts is that you need to use eqmod for them to work. This im sure everyone is aware of and shouldn't be an issue. I got my parts from this site before they offered it as a kit.
http://www.beltingonline.com/heq5-be...rive-kit-12097
Goodluck with your mods.