Well, I solved my problem by chucking a 50 ft. cable out of the 2nd story window (because packet loss is for sissies), but here is a summary of my research:
If you can get everything on 5 Ghz that should help a lot. Beyond that, if you get a high-gain (usually 1-2W) antenna, you probably want a directional antenna. A high gain omni antenna will probably just bounce around more, which would boost signal strength on the same level of the house, but might diminish range through walls and such.