Christian, I believe the biggest benefits to the upgraded lower section are the stability/ rigidity of the bolt together frame, and the slightly greater Z- height gained by dropping the belt and carriage components. Becuase I built the 80/20 style 5-bolt joint plates w/ leveling feet in the middle to use on mine to stiffen it up, I don't think I will be doing that portion of the upgrade until I do my rev 3 bed re-design. That probably won't be until after the new year at this point.
I hope to be assembling my dual head this weekend (just have to print the fan shroud). I was waiting for Gordon to post a new set of files for the upper end components with the few issues addressed that people had mentioned on the forums here before I jump down that rabbit hole.
As a side note, I found a bunch of aluminum framing cut offs in my garage that I'd stashed after our Solar install earlier in the year. Think I may use that to mock up the H-frame that I want to try for the rev3 bed before spending on phenolic or V-slot. It's a bit heavy, but should at least give me an idea of if I want to pursue the H-frame idea or a solid phenolic plate.