High-speed hdmi with ethernet vs. without ethernet?

The ethernet part isn't really anything special or add anything. It's just a part of the spec that allows a network signal to be passed over the cable, if both devices support it, so you could supply a TV with network access over the HDMI if the TV and the PC supported it. It's probably barely implemented anywhere.

My local dollar store sells HDMI cables and they work fine for me. I've never been a fan of overhyped expensive cables.