hahah a difference in play, no, if you're that nuts about the signal, reflash a WRT54G with linux firmware (tofu6 if you have a v4 the latest) and boost the signal coverage, or do what i'm doing which is a wifi router downstairs then a wifi router upstairs receiving that signal and boosting it then spitting it back out.
Wired is wired, there's less lag if you will because there's no interferences, it's a direct connection, I play with wifi on Live, and have no problems, but I don't have that many walls, waching machines, microwaves, cordless phones, etc that could disrupt the signal, which is something you have to consider. Also going to Gamestop or EbGames for a cable isn't the greatest idea, they overcharge and it's low grade. You're better ordering a cat5e or cat 6 online, however you will experience lag if it's over about 100m (i believe that's the distance)
Ozy is right on another fact too, 54mbps is WAY WAY faster than your average cable/dsl provider, I may get 1mb down or maybe 2 down at most, that's on a good day with no one else on, the extra is mainly for network filesharing. Buy some high-gain antennas for your wifi router, that would boost the signal as well.