Yep aware of all of that. I have a 2x2 connection at the moment on 5GHz. It's only from one floor to another directly on top (albeit through a concrete slab).

However as mentioned, I'm not sure this will actually make much difference due to MythTV's buffering. I've been meaning to run a wired 100Mbit (or maybe even Gbit) just to try it out. If that's no good, WiFi is no chance...