The highest I've used is 32-bit, it sounded perfect. A couple of years ago one of my professors told me equipment existed for 64 and 128, I assumed by now it was being used regularly in high end studios. I used to record at 24-bit 11 years ago in my bedroom. It's good but I don't see the point in using another format that we'd kick ourselves for using in a few decades again (24), like what we did with the cd. I admit 32-bit is fantastic but I don't see the point in not using the best available if people might call us idiots for passing on it a hundred years from now. For sure they will think we were crazy for thinking 16 bit/128 mp3 is good enough.