1 road bike (simple, light), 1 TT bike (could be more aero, could be lighter), 1 all-weather commuter and winter bike, 1 Monark 828E ergometer indoor bike
Yes, but it's not that simple to do just like that.
To be able to get a decent estimate, you'd need to provide:
body size (seen from the front)
tyre size and tread
wind speed and heading relative your direction of travel
Even then, I'd say the margin of error is probably 30% or so...
www.analyticcycling.com has a power calculator that can give you a ball park figure
for a road bike. If you can find a shop with a computrainer set up you can see what you can do on a stationary bike. Doesn't really help a lot but it is interesting. On the Giro recently a couple of cyclists had power meters on their bikes with remote readouts that were occasionally displayed on the screen and a few years ago on the HP ladies tour in Idaho, one of the ladies had the same and was running 200 to 400watts (400 were chases up short hills to reestablish contact with the peloton).