Hey Sflinux,
I just posted another review of the new Phase5 Prop I am riding (inspired partially by your request for a review thread
). According to Bob Smett's, owner of ZAP, this board is identical to the Zap Large Pro model except that the Prop has a single fin option. First I have not seen your board, but just based on the dimensions I think it would be a bit too small to be a light wind machine vs. your Placebo. I weigh 160 lbs, and the Prop I ride a 54" x 20.5". Also the new Prop I have is about 3/4" thick vs. 1/2" - so it definitely has more volume than my old one. I think the low end of this board would be better than your current skim for certain. I can tell you that I ride both the Placebo and the Phase5 regularly and both boards have the same low end for me, which starts at about 10. However, I cannot say for sure that you will find this to be the same for you. Also, at this year's Surf Expo I saw a 57" x 21" board at the ZAP booth. Who know this might be the light wind skim that would be ideal for you.
What wind do you generally want to ride in with your skimboard? What wind speed do you like to ride up to? Also, where are you located maybe there is a dealer in your area that might let you try before you buy? Let me know and I can find out for you.
Check out the review here and let me know what other questions you have or I can help with:
viewtopic.php?f=3&t=157&p=720#p720