I went around the block a few times with this issue when I first got back into using hardware again (I swear that Win 98 running Octamed had tighter timing than XP)!!!
1) Sorry to break it to you, but Renoise just isn't very good with lots of MIDI. I ran tests on 3 different PC's against Cubase SX and Dreamstation and Renoise was just totally pants with whatever interface or PC I used. True story. Don't get me wrong - I love the program and have paid twice for the registered version over the years, but it's not a goto sequencer for MIDI. Sincerely wish it was though...
2) The best timing I've gotten using an XP PC is with Cubase SX and the MIDEX 8 interface. Totally rock solid.
All sequencers / computers seem to have a different 'vibe'. I also ran tests with an Atari ST and Amiga. I honestly think that the Amiga running Octamed had the best 'vibe' out of the lot. Nice solid timing but also something else happening there too - just sounded more 'organic' than the Atari or PC. XP and MIDEX is more practical, though
3) Windows generally sucks for MIDI - it's true. Tracking + MIDI + Windows is currently a non-event. If you *must* use a tracker with MIDI, I'd have to recommend the Amiga + Octamed.
Good luck. 
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