At the moment I can't think of an explanation. It's really wierd if the wireless always keeps up.
I don't think it will be the ethernet cable, but is is worth unplugging it at both ends then reconnecting it.
Are both in use most of the time, or is one of them just in the evening? Just wondering if the ethernet gives up if the wireless is in use. It shouldn't, but!
Thinks ... if the wireless is streaming video or TV catchup, or heavy P2P then that sort of thing could be getting priority and slow the other machine, independent of how it is connected. P2P in particular can swamp the upload so the PC downloading isn't able to give the ACKs.
Similarly if you have P2P running on the PC, even if you aren't downloading yourself, someone else may be uploading from it. That could have the same effect but leave the wireless from the router happy.
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