The biggest concern I have is that there are coverage holes for even just voice calls surrounded by 4G towers. I know they have to build out new towers to cover some of those areas, but you would think that would be a priority to at least get voice coverage. And no, many of those dead zones have zero roaming options. When you struggle to get better than -95dbm good luck if you stand in the wrong spot to make a call.
So LTE does no good if there is no signal to begin with. Where there is LTE the speeds are good. Unless 800mhz can magically go twice as far as the current signals can, Sprint will have some patching to do just for voice.
CDMA 800 will help the majority of the voice coverage issues. From my experience with sprint in the Jacksonville area voice coverage is stellar the only issue I have is with signal strength inside of buildings (low signal or no signal). Other than that voice is fine.