I should have clarified that I currently own a 4k tv, but intend to eventually upgrade to a larger model. I have a large room and sit about 14' from the monitor. If I go 1080p I can probably get a nicer, larger tv that much sooner without breaking the bank.
The build quality is the most attractive thing about the 4520 for me. It's a beast and that price is pretty fantastic for what it is even still. If I understand correctly there could possibly be occasional issues with not having 2.2 and it's a little behind, but still relevant enough? I'm still slavering over it though. I want that amp section.
On the other hand, as you pointed out, The 4200 is more current and no slouch itself. Decisions, decisions. I'm kinda waiting for HD to pop in too. He has one, and he's the one who kicked me down the rabbit hole at the beginning!