Interesting, a minimum wingspan limit this year. Those are going to be heavy models compared to a couple of years ago, since the high Cl(max) airfoils that have been popular are Reynolds restricted (min 200,000 for the 1223). That would mean a min chord of about 12" @ 25mph...and a min wing area of 1400 sq" (12"x10'). Bring out the composites folks!
Late to join the discussion, but I found SoarNeck's comment interesting. SoarNeck's span and cord for competition and Re driven minimums result in an AR of 10. I haven't crunched the numbers and I'm not sure how the competition has gone in the past, but 10 doesn't sound out of reason when working the compromise between strength to weight and induced drag.