Funny you should ask. Yesterday I was tweaking a dual Athlon with 2 SATA Raptors in RAID.
At 44.1K and 24 bits, I was able to play back about 220 tracks with 150 RenEQ 4 on inserts. This was tested at 1024 samples buffer size on 2 RME HDSP 9652. That's where I would sit if I were mixing pure Native.
Pulling the latency down to 128 samples for liveable (though still not great) latency has a big impact. Big. Though on that system, it would still be decent track counts.
My rule of thumb for Native DAWs, assuming you want to make music without tech hassles, is that your Native DAW should be able to do *at least* double the tracks and plugins you will ever really use, at a given latency. At least double. Sure, you don't absolutely require that headroom, but any device with as many variables as a desktop computer will from time to time unexpectedly use more resources. For smooth workflow, leave yourself as much computer headroom as practically possible. That's why I'm such a fanatic about computer speed. Faster means smoother and less stress on the system. Over time, that equals a lot more fun and a lot less cussing.
Sorry I can't give too many details on tracking latency, since I'm not a big fan of that and never do it. Fiddling with the buffers or doing the Direct Monitor workaround while trying to record real people with real microphones is not my idea of a good time.
And now I get a spanking from the Native champions.
Regards,
Brian T