My XP-M 2500 will drop to 1.1v @ 60Mhz FSB.
Unfortunately my NF7 board doesn't seem to like dynamically changing the FSB. It will drop just fine, but occasionally BSOD's while attempting to raise the FSB back up. Seems to be a fault particular to my motherboard; it did the same thing with an XP2100 CPU, yet many other people report good success with the program on their NF7's.
If you've got a motherboard on the compatibility list, I highly recommend trying the program out. It's very slick, and gets better with each revision.
I have an AOpen AK79D-400 Max board that could dynamically change it's FSB with SpeedFan with an 1700 T'bred 'A'. I then upgraded to a Barton 3000/200. It will now go down 1-100MHz on the FSB but locks when it tries to raise it, at all. I was hoping it would help keep the box cooler, but oh well.