Check this recent thread for a bunch of good ideas:
Depending on what you’re trying to do, it might be better to just enable/disable the individual synths. In general, my understanding is that all VST’s get loaded when a song loads, so unless your states are loading different sample sets or complex presets, it should be close to instant… it generally is for me.
It is strange that something worked faster in C3 vs C4, though I think that’s a Brad discussion.