Why not the 55" 8K?
Also the checkerboard is because you're not using variable refresh rate. You need to turn on game mode for the TV and VRR in OS display setting.
I can't find any. The newer QN800D or whatever aren't available in 55". And they don't make the QN700B anymore.
EDIT: Also wow I've been using this QN800A for like 3 years with the checkerboard problem without realizing that enabling variable refresh rate solves the problem. Thanks for the pro tip!!!