Funny, I was just working up something for this forum area to post. Go with 155cm or less (my longest travel board is 157cm). Slingshot now came out with a new board, a 141cm SX:
I'm going to be switching to this board since it is supposedly faster than my 157cm board, and planes up earlier. I'm 6'2" and 185lbs, so we're about the same.
For travel, I limit my luggage to one kiteboard bag that is as short as possible to fit my longest board (157cm). I leave that separate so its as light and thin as possible. Then I pack all my kites, scuba, wetsuit, etc in a large hockey duffle with my clothes. If my girl comes with, I have her pack two large roller luggages with all our clothes and stuff and I put here kiteboard and extra kite in with my stuff and it gives us each two checked items and one carry-on can be left over for whatever else I need.
If the airline says anything, I say "its a snowboard bag". You can also say its a knee board. Then say, your website says it within limits and act confident. You should have no problems. NEVER say kiteboard, or surfboard or wakeboard, you will get charged!