Was that 360W measured using a powertap or Strava? Either way, that's a very, very respectable effort. I find the best 20 min efforts I've ever had were uphill. Being a smaller, lighter guy, I can't seem to push as hard on the flats. I'm sure you're closer to 380 uphill at the least. I wonder what your coach would have to say about that. I think power is pretty absolute. Meaning, you should try for your best effort from which to baseline your intervals. Perhaps give it a whirl on one of your local climbs?
What kind of power to weight FTP do you have? Have you seen this: http://home.trainingpeaks.com/blog/article/power-profiling ? It should give you an idea of how you compare with category amateurs in the US as well as give you a sense of your type (sprinter, all rounder, TT etc.)
This is an estimate just based on what power friends (much lighter than me) are knocking out when we ride side by side during training.
Got it Andy. 335 sounds like a reasonable number given that most FTP tests go for 0.95 x the 20 min power number and you went for 17:24.
The side by side thing is really tricky to rely upon. For example, the last "fitness/FTP test" I did was on a 14.6 km course (flat, but out and back), standard road bike, and I averaged 37.8 kph for 24:40 but only used 273 W according to my SRM. So your 1 kph advantage comes at an extra 87 W! That's a chunk of power. Aerodynamics has a lot to do with it. Best 20 mins ever was 321 W but going uphill. What I would do to have that number for a threshold.
Andy, the Power2Max meters are substabtially cheaper and the Type S appears to be just as functional as the Quarq and SRM. There's no Japanese distributor but you could pick one up when you go back to the UK.
I did an FTP run along the Arakawa a couple of weeks ago. Not as "pure" as on a trainer but the path was empty enough for me to get some numbers. I'm still some way off what you can put out so will have to rely on being a bit skinnier!
I do my testing on the morning course at Saiko in Saitama, which has short risers, and downhills of river banks, and one time I come to a complete stop to turn around. But it doesn't really matter, because what is important consistency. As long as I always do it there then I should be able to gauge improvement.
Doing one off testing outdoors with borrowed equipment doesn't really tell you much, unless you can borrow the same equipment and use it in the same location particularly with the same temperature.
My 20min is about 320W, 60min is about 300W, 120min 280W. It may be over or under depending on the day.
Golden cheetah has bunches of interesting info for analysis. Free software you can download.
I love mine, cannot imagine not having it on my bike, just makes hammering it out more challenging, and rewarding on a personal level, and therefore fun.