Another possibility, which I am considering for my next setup, is two seperate 8 horse singles both driving the same "oversized" generator. Run two when you need lots, and one when you don't. That also gives you some backup protection in case you have a bad event with one engine, you're not totally without juice while you get things fixed up.
I just haven't figured out the slick way to easily drive one or both or either at a moment's notice.
Finest regards,
troy