@Paul to answer your main question, I've been a RocketTheme user for many years. If support was your main concern I can tell you from reading their forum the past two weeks for Gantry 5-based questions, I haven't seen any change for the better than what you've experienced in the past. It may quiet down over time but right now there's an influx of support requests if for no other reason than Gantry 5 is new and people have questions. You might find the support culture hasn't changed even if the framework has.
Coincidentally, I took a few days last week to review other templates with the advent of Gantry 5; it seemed like a good time to pause and look around (especially since the Requiem template introduces a problem/conflict with JQuery). So I looked around, albeit briefly, at sites including JoomlaRT, JoomlaShine, and Yootheme. For my aesthetic, Yootheme seemed best; they caught my eye in a performance test I saw at
JoomlaSEO which showed them the winner.
I don't yet have objective data, but loading on my private server it's clear there's a big difference in load time between my old template (admittedly this was G4, I only loaded ES with G5 before abandoning it) and Yootheme is immediately apparent. I haven't had the need for any support and maybe my opinion will change later, but right now I'm happy with the Yootheme template (ease of use, aesthetic, and performance) and I'm hoping RokSprocket will run well there as well using EB as the content source (I'm pretty sure it will).