BRSracing summed it up. I'll add that Sanwa RX's are spendy compared to $37 ones you can get for the 4PX, along with the 4PX menu screens being easier to navigate, IMO.

I ran my 4PX for the first time coming from a DX4R this weekend, hands down a better feel, IMO.

DX6R, never held one. A guy next to me on the driver stand was using one in a qualifier. He didn't finish the race due to "radio issues".

I've run, and supported Spektrum radios on this forum for years, but the 6R is simply something I would not recommend at this point. Horizons top Pros don't even seem to run it, that says something..