You can get a baseline power from Strava for ball parking. Pick a popular segment that has a decent gradient to it, this will reduce the effect of winds. Then look at the leaderboards by weight in your weight class and find someone close to your time that has a power meter. Overall, it doesn't matter what your exact FTP is, if you know your heart rate zone, just train on them. To gauge your improvement you need to find a hill (like above, good gradient to reduce wind effects) that takes ~20 minutes and just compare times. I'm not going to pretend to know your situation though, so be careful.
Also the power is a over time thing, 4 w/kg is excellent for an hour, pretty good for 20 min, ok for 5 min, and terrible for a minute. But I wouldn't concern myself too much about it, personal improvement is the goal.
I apologize about the weight, I thought it was just a flippant remark. Generally in the off season, when I'm riding I don't put on much weight, and I eat horribly and often. I can see how that could be a real problem if you can't keep your intake up. Yeah, you don't want to be so skinny that you have no reserves for recovery.
Also join our Strava group!
http://www.strava.com/clubs/bikegaf