Interesting.
I'd guess there's another factor that also determines ultrapeer status (like other faster/persistent ultrapeers with available slots in your node?).

Actually, you shouldn't see much difference as far as searching, uploading, or downloading when in leaf mode. With 128 kbits (16Kbytes) of upstream bandwidth, it's probably better to run as a leaf, since an Ultrapeer can use 7 or more KB/s just in gnutella traffic.

btw--the tools->statistics is the best way to see LW's bandwidth use