In my experience wired cat5 or cat 6 is "dozens" of times faster than Wifi - whatever theoritical speed it can do, local conditions such as other networks in the vicininty normaly trash Wifi expected performance. I've got a dual channel N router that should be capable of really fast downloads (from my NAS). But using the cables makes things scary fast, whereas using wifi is unbearable.
As a practicle example... - I keep my ripped DVDs on a NAS so I can watch them in any room, and normally copy them to the desktop before watching so I don't get jumpy playback. Last night I forgot to plug the cable in my laptop and after 5 minutes the Wifi connection was telling me there were 20 hours left to transfer the file. Stopped the transfer, plugged in the cable, recopied and 90 seconds later it had transferred a 1.7GB file! That's what I meant by scary! There are about 20 other wifi networks that have at least 1 bar signal my laptop can detect. MI'm using a time capsule which has selected the least congested frequency (and is on a different channel to all the other networks) but there's still overlaps in the specturm. The cable is CAT5e running connected to gigabit ports. I'm about to move from a rented flat to an owned house - and will be CAT 6 cabling the new house based on my Wifi experiences.
So the answer - forget WIfi and use the cables. Wifi is fine for a bit of browsing and background backups, but if you've got lots of data to transfer, plug in the ports.