For Octopus:
You can set affinity, you can set any of the config values per instance I have all mine set to 15 which seems fine for now but I may try tank and healer on 2 cores and 3 dps on the other 2.

Against Octopus:
Yep I use cast sequence, normally for interrupts or slows, but that means adding a /stopcasting at the start of the macro causing all of the toons to stop (rather than the one who is 'up' in the sequence). With KeyClones Round Robin only 1 toon would stop, the others would continue their current cast.