I ran on a treadmill at the Westin in Boston last week and it estimated my power output to be about 315 W while I was running at 9 mph. 9 mph is a speed I can hold for about 30-35 minutes on a treadmill. I can run a bit faster outside, even though the consensus is that running on a treadmill is easier than running on the road.
As I mentioned before I agree with that statement, for short distances. I can certainly run at a faster speed on a treadmill for short periods of time, but I cannot hold this for very long. The reason I believe is lack of cooling. I am probably relatively inefficient in that I tend to generate a lot of heat and sweat a lot. I certainly sweat a lot more than other people around me, and it is not uncommon for me to leave a sizable pool of sweat behind after a long stationary workout.
Yesterday I rode on my rollers and I held 325W for 30 minutes (in aero position). I would not call it maximal effort but it was up there. What I like about this is that numbers are nicely consistent. It appears that something in the range of 315-325W is what I can hold for about 30-35 minutes. According to the lookup tables that would correspond to a speed of about 40 km/h (24.8 mph). The real speed is likely higher since this was done in a deep aero position.
My speed on the rollers was lower but it is a rather arbitrary quantity and depends a lot on the setting on my Kreitler "Killer Headwind" fan.
On the standard 20 minute test I can get a power to weight of 4.2 or better (mid Cat 2 range), but so far I have never gone all out on such a test so it is possible that I would do even better.
On Saturday and Sunday I rode a 35 mile loop through Orinda, Moraga and over Pinehurst. On Monday I rode on rollers, including the 30 minutes at 325W. Today I ran to Montclair and back for 8.8 miles. All I can say is that this time I felt a whole lot better than last time I did that run.