The problem arises when needing to know how frequently to checkpoint, i.e. the size of said blocks. If I am running the emulator on a machine 200x faster than the emulatee, the check should be every instruction because we have the time and executing too many instructions between syncs will be very noticeable. But if I am running the emulator on a machine 1.05x faster than the emulatee, we don't have a lot of time to work with, so you'll guess at the block size between checks? Get it wrong and you've done too many ops or too few. Either way, you definitely don't have time to sleep or use small block sizes. I'm sure I'm over thinking it.