I find:

20knts is too windy.

15knts is doable. 10knts preferred.

1m of swell (swellmap) is doable

1.5m swell starts to get uncomfortable but it depends on the period.

damien

http://www.seafriends.org.nz/oceano/beaufort.htm

The Beaufort has a good visual indicator of sea conditions vs wind speed.

Personally, I don't venture out (fishing) if its forcast to be more than 15kn as it ceases to be fun for me (although if it roughs up while I'm out there, I'll stay put and fish a bit longer).

However, for general faffing around in stroppy water and having a great workout of physical and mental agility - you can't beat a good 30kn wind within the confines of a bay with a safe runout!  Punching through chest slappers for an hour will give you a great nights (or afternoon ) sleep, and you'll find your spatial wave balancing abilities will also improve - as will your self rescues.