I am going to say that I did not read though all of the posts, but hopefully something I say here won't have already been brought up and you'll find useful. There is no way that I would ever do dual exhausts today without a H-pipe. The reasons and benefits are simple. Balance.
Here's a story as just one example. Years ago a customer came in with a Dodge class C motorhome from the 70's. Complaint was constant overheating, and smell when going up long, but not necessarily steep hills. And vapor locking. Tried a couple things with no luck. Long story short turned out his new mufflers, did not flow the same, this essentially caused exhaust gas to be constantly going though the crossover in the manifold and heating everything up.
I could go on with examples, but an H-pipe will cause your engine to be better balanced in the exhaust and may make it last longer.