It really is a function of what is blowing through. If it is a particularly powerful cold front and it goes for a few days, you can get some large seas. Usually though it is around head high or less. The 13 m may serve again, unless something stronger blows through, then it would be better for your 10. It is so hard to say in advance. It is warmer in the Keys still, I about froze my butt off there in a 4/3 some years back in a particularly nippy cold front. If the wind is out of the SE or E, it is usually warmer than if it is from a northerly direction, in the Keys and in Delray. I would plan on a road trip regardless to see more of what South Florida has to offer. Hope you have good weather for your visit.
Here's an old write up on Key West:
http://fksa.org/showthread.php?t=468
and an interesting video from KW and the lower Keys: