Time Machine - Effects of Disk Interface Speed?

I was wondering what folks' experience has been regarding the use of
various disk interfaces to the Time Machine feature.

I've run USB 2.0 and Firewire, but have not really noticed much of a
perceptible effect on performance. Has anyone noticed any real
difference when using the wireless Apple product?

It seems as though TM does its thing in background pretty efficiently,
and variations in the interface aren't that noticeable in most cases.
Maybe unless the particular backup has to update a fairly large amount
of data? Or if one is performing an explicit read or write to the
drive being used for TM.

Has that been others' experience?

Thx!
.