Ok, I almost forgot I had chicken soup on the stove simmering away.
Quickly, I was reading interesting articles on SOS site 3 part + other articles. Anyway, the CPU hit on older processors can peak @ 50% for the Wavestation but on newer processors it shouldn't go any more than say 25%. Poly6 moreso. The MS20 has a CPU Loading Threshold that can be set. The M1 is good though with 8x multi and the IFX it will of course add some CPU overhead. *Phew*
OK, this time I've got to go and have my desserts.
Edit: Just got back to add links -- these are 'old articles' but most of it still relevant:
Korg Legacy Collection Part 1 Part 2 Part 3
Update
M1 - Collections (Sounds) seems like they also included the kitchen sink....

So, newer systems should be adequate enough to run the MI, Poly6 and WaveStation simultaneously.
Both the M1 and WaveStation are 8x Multi-Part.
IIRC Korg hardware, the sounds are quite rich and useable. Though I mostly recall the M1 and Poly 6, but I do trust that Wavestation is also pretty darn good after listening to demos on YouTube.
It's also cool that Modulation and Arps can be sync'd to host and it's easy enough setting up CC.