still...any wobble at < 25 mph, flat or downhill isn't right

Last night I tried holding the top tube with my knee, and it worked! 30mph with almost no wobble. I still think it may be my fit issue, or the roads being bad.
As far as the wheelset - it's a brand new Easton Circuit with less than 100 miles on it - perfectly true.

I agree that 25 is pretty slow for a bike to start wobbling. You should have the bike/fit checked out at an LBS. I can only imagine what would happen if you did a proper decent (i.e. 40mph+).