Personally this is what I started to make a long time ago and then got too lazy to complete.
I think this is the more sensible option, but I suppose it's just a matter of preference
Some people do have really shitty connection/hardware, but just because the trainer has the capability to run two SWFs, doesn't mean that they're forced to use that capability.
I don't think it would make a difference - but maybe run some tests. Maybe try running two instances of Grimoire, and then try running one instance of Grimoire but with the 2 SWFs. I don't know how you'd go about seeing which variant uses more CPU on Windows, but it's possible on Mac so there'll be some way (which you probs already know how to do bcus ur smart).