Using Time Capsule JUST for back-ups (not as a router) ..

good question, i would like to get one of these just as a wireless back up and not use the router atleast until mine dies.

 

The 802.11n speed will only be obtained if you directly connect to the TC, meaning you'd have to have a wired connection from your router to your MBP.

 

The TC should be able to be set up to provide wireless access without doing the router-ing itself. I.e., your router does the DHCP assignment, but the TC distributes a wireless connection to your local network. If you do that and connect wirelessly then you can get N speeds. And if connect with a wire, then you'll get gigabit speeds, not just N-wireless speeds.

Check apple's website (or search here) for a thorough configuration guide on Airport Extreme/Express and Time Capsule. All the possible configurations are covered.

 

http://manuals.info.apple.com/en_US/Designing_AirPort_Networks_10.5-Windows.pdf

Set up the Time Capsule in bridge mode, set the radio to "802.11n only 5 GHz", give it a unique SSID and you're set. The plus to this is that any computers connected to the b/g network broadcasted by your router will also be able to see the TC's HDD and back up to it.