I think it really depends more on your comfort level. I had my disk wheel on in winds of about 20mph last weekend and rode for about 30-40 minutes just to figure out the characteristics. I found that it is not that bad as long as you relax. Somtimes you need to put the power down to right the bike, but you need to keep the arms relaxed.

I had a H3C on the front as well.

I am no expert but everything I have read suggests that aero wheels perform better in crosswinds.

Well - I know very little about cylcing being new to the sport (last was my first year doing tri's) but I am an aero engineer so I'll throw down a bit. As far as drag goes for just the wheel itself, disc wheels are always better than standard spoked wheels or anything in between - regardless of crosswind. In fact, disc wheels actually have less drag at high crosswinds than they do with no crosswind. A disc wheel is basicly a symetric airfoil and generates a small amount of lift if the relative wind is at an angle to the direction of travel. At high relative wind angles (30-50 deg?) this lift in the forward direction can actually be equal to *or greater* than the drag produced by the wheel. The downside is that at those angles, the side forces are very high, and it is the side forces that reduce your stability. Keep in mind, the above is only true for the wheels themselves, your body *isn't* a good airfoil and thus doesn't generate much lift. As far as the body is concerned, relative wind angle increases the exposed frontal area (relative to the wind) which means more drag - my guess is that the increased body drag will far outweigh the reduction in drag of disc wheels due to their lift.

Here are some more links on the subject:
http://www.cbss.ca/tip11.htm
http://www.richardpettinger.com/cycling/blog/archive/2007/02/23/improving_aerodynamics/view
http://www.sheldonbrown.com/brandt/wind.html

Also, Dave Warren talked about this on a segement of his podcast "TriTalk"... you do all listen to tri talk...right?!
http://tritalk.podshowcreator.com/
(Episode 19 at the bottom is the one you want)
The above link is to the episode download page - if you want to subscribe to this podcast, use the following: http://tritalk.podshowcreator.com/feed.aspx?feedid=371

Hey, engineer geeks! Tell the masses why we don't put disk wheels up front (you only see them on a track).

And another point is that you will only gain the true advantage of the disk wheel when you are tucked solidly into your aero position.

About the only time I don't use my disk wheel in a race is when it's quite hilly, but even then I think it's just something I need to get used to, but I don't want to look like a dork training with the disk on the back. I did ride the IMWI course once with the disk on, and that was one helluva ride on the downhills.

because the steering column can rotate, the above mentioned side forces would throw the steering around to much, the disk would act like a giant sail, meaning you would go where the wind is blowing, hence you run the risk of at best Zig Zagging down the road and at worst being thrown off.
There are no crosswinds on a track so you can use them to really wind up that speed.

I have also personally seen two guys in my age group blown off the course while on discs, both happened right in front of meat different points on the course. One guy managed to save himself, the other ended up on ground.

Of course, the race was the DAY after a hurrican blew through, and we were getting some serious backlash from it. Steay 15mph winds with STRONG gusts.

Not to say they cant be handled with practice, but I would go with say 60mm or shorter rims on a gusty day.