In the shape I'm in now, I've been up to 24mph on the flats for a brief period. I used to be able to hold almost 30mph for 2-3 minutes. This is on my DF.
On my new 'bent, I've been up to about 18mph on the flats. I'm building my new muscles.
My two fastest downhills were coming down from Paradise on the Chico Wildflower-44mph, and coming down the east side of the coastal ridge on the Marin Century-46mph.