I’ve done tests “multitimbral VST with midi channels” vs “multiple Instrument tracks”. There is a difference, although it’s not dramatic. A more heavy stuff like Omnisphere or Battery 4 sure eats more CPU if you load 10 instances instead of one multitimbral. But i still do many Instrument tracks because navigating through VST Rack and doing multitimbral automation takes a lot of time and mental powers.
If you don’t mean multitimbral stuff, i think there’s absolutely no difference, especially in 7.5, because now they got almost the same.