I didn't find the solution, I only implemented it
This is holy grail for emulation latency! Supposedly impossible to do..
There is still something unexplained going on.. I see bottom slice color appearing in the very top of screen even when topmost present-call is guaranteed inside vblank period.
Test with sound disabled, it should remove all large (as in more than +-10 pixel) random jitter but it does not..
Warp mode should already work (and works even better now). Fastest possible CPU still won't work, it is always the biggest problem..
Slice count 2 (from 3) is now supported.