etracer--
Fantastic work! This is just the analysis we were looking for and just the result I hoped for. I will generate a new official version of NewSoftSerial shortly incorporating this and some other improvements.
I agree that there is some chance that this will affect bit timings. I have a fairly elaborate test suite built here that tests all the supported baud rates from 300-115.2K, so I should be able to make some tweaks to compensate, if needed.
Ideally, we could conditionally compile this code, because putting it in all implementations means that the Windows interrupt handler will always be slightly slower than the OSX handler.
Thanks again, and congratulations on the fine work!
Mikal