I have one of the new dual-band Time Machines BTW.

I'm running 802.11n on the 5GHz band with wide channels. In fact I keep the TIme Machine set to restrict n to the 5GHz band.

Network Utility reports 270 Mbit/s link speed. And during the copy it reports no collisions nor errors.

If I set the radio on AUTO, which allows n on both frequencies, I can get an average of 4.8MB/s running n on the 2.4Ghz radio.

If I set specific channels instead of leaving that on AUTO like it's always been, it seems I can get the 5GHz radio up to about 4MB/s using channel 36 - I'm testing the others now.

When I set this up a few months ago, the benefits at 5GHz were obvious over 2.4, with consistently higher throughput.