This indeed is a different problem/topic. Let’s not mix those discussions please.
What are your audio settings in Renoise you’ve tested this with?
MIDI output timing indeed and unfortunately is quite a pain to get right on Windows, compared to OSX and Linux where it usually just works, as there rarely is driver-side MIDI event scheduling available and applications have to work around Windows high timer resolution. I hope this changes in future, as it did with WASAPI for Audio in Windows 8.
In general: as you already did in Reaper, using small buffer sizes and ASIO will improve the MIDI timing in most situations. The smaller the latency/buffer size, the more stable the MIDI output stream should get on Windows.
If you can’t test with ASIO in Renoise, I can create a version for you which does, so you can test out if this solves the problem for you. Please contact drop us a mail at support @ renoise if you’re interested.