Some quick thoughts - disabling multi-core support in Kontakt has been the way to go for YEARS, so I support Rumdrum!
I also believe there is no processor difference between rack and instrument tracks. There IS a difference between using 1 Kontakt instance per instrument (the FORMER instrument track paradigm) and multi-timbral instances of Kontakt (the FORMER rack instrument paradigm), which is why there may still be some lingering perceptions that instrument tracks are less efficient. But now that instrument tracks can function in multi-timbral mode, performance is more of a matter of how many Kontakt instances you have.
THAT ALL SAID…
You basically have 3 options - rack instrument, instrument track, or VSL Ensemble Pro. Performance depends on whether you run Mac or PC. Cubase is much more efficient on PC than Mac, unfortunately.
If you run a Mac, the most efficient use of resources is VSL Ensemble Pro. You’ll get more Kontakts loaded in this way and tax your system less. Disadvantage is that you’ll have very complicated routing and a total pain in the ass to automate FX and such due to midi and audio being split on separate tracks. If you’re not using VSL, rack/or instrument tracks in multi timbral mode will get you almost as much horsepower as VSL. Instrument tracks with one instance of Kontakt per track will get you the least amount of performance (mine tops out around 60 instances).
If you run a modern PC, I’ve heard Cubase can have 100s of Kontakt instances, so it seems using VSL is not a requirement.
Couple more things - Kontakt can “overload” indepently of Cubase, which is what might happen if you have, say, 16 instruments on 16 channels in one instance of Kontakt (i.e, using it multi-timbrally.) But I find this preferable to overloading Cubase via tons of individual instrument tracks, because in that case Cubase becomes sluggish and unstable on top of the pops and clicks.
Anyway, the above performance issues are why I had to switch to Logic for a TV show I’m on. We got sick of using VSL Ensemble Pro (the automation complexities are just too hard to live with) and we could not get our template loaded into Cubase as instrument tracks. Logic has a more efficient engine however, and we WERE able to get the entire template loaded into it. The difference, btw, is night and day - I’m talking 5% CPU usage in Logic vs 70% in Cubase. We suspect this is because Logic has the power to “deactivate” plugins dynamically that are not being used. Cubase doesn’t seem to be able to do this, at least on Macs.