getting mixed up, need some help with length

hi,

i'm a guy who's 5'6" tall and weighs around 135 lbs and aside from really wanting to get a wakeskate so badly, i'm also mixed up now coz there are still a huge variety of boards to choose from, even though i've tried to narrow the gap...basically i'm not yet quite sure what size to get...coz i've seen all kinds of sizes from 40's to 41's (which i believe i prefer), which just gets me thinking twice about each board all the time. Although i definately know that i really want a 3D concave, its just the length that i'm concerned with... so can anyone please suggest the ideal length for me? thanks alot.