Well the connection rate (not to be confused with speed) doesn't really matter that much unless your transfering files from one computer to your laptop. If your just talking about internet speed, almost no effect what so ever, as long as the connection rate is higher then the download speeds given by your ISP. Now if you do network your computers together, and your laptop was connecting at 5ghz N then your transfer rate (from 1 PC to another) will probably drop by half. But its hard to say. Its really important though that you look past your connection rate. Its like comparing RPM of cars, usually meaningless unless you have very specific needs.
With that said, and if those are your needs, you may either want to:
1. Look into making one of the connection wired.
2. Buying a ethernet wireless adapter for the 360 that can connect at 5Ghz N. Dlink doesn't have anything that offers that, but maybe the
WGA600N. That wouldnt be supported by this forum ofcourse. :-)
3. Buying a router that can do 2.4 and 5Ghz at the same time. The only model Dlink makes is the
DIR-855.