FWIW, a glass cutting company published that you should not exceed something like 200RPMs when drilling glass with a diamond hole saw. i can't recall why, but that's what i did. very slowly and hardly any pressure. i was too affraid of cracking my new 55g tank. 3 holes went nice
just that the hole saws werent 100% true. they wobbled a bit. i even bought a new drill of a different brand and corded, and it still wobbled. oh well.