I was using Wireless N, but I run Quicken for Windows on XP within Parallels and, as Time Machine treats the whole disk image as one file, back-ups were taking forever and slowing down other wireless-based activity. So I hooked-up the iMac via ethernet (relatively new Cat 5 cable) and that made things much better, but the cable I was using isn't long enough. So today I bought a longer cable (25'), which is Cat 6, and just wanted to make sure that there isn't a setting I could tweak to use the extra "space" on Cat 6.
FWIW, I've finally succumbed and bought Quicken for Mac, and will be cursing the Gods later while I convert. Quicken is the only reason I have XP on my Mac, and that's a 70GB image that drags down back-ups and takes up too much space on both my Mac and my TC. I downloaded the QFL Beta, but that cannot import from Quicken for Windows, only a Mac file will do. As Intuit are about to cut off online support for Quicken 2006, I had to buy a new version one way or the other.
This way, I will suffer Quicken for Mac until QFL is ready, and I will have a Mac-based Quicken file already for the upgrade. In the meantime, my Time Machine back-ups will be a lot smaller.