Don't have much experience with the LEM, but thought I'd give you some insight about the 50's. I bought my 6 year old a Suzuki LTA-50 in Feb '02. worked great in dirt and duning around camp. Shortly thereafter, he wanted to start riding with the rest of the group out on the sand highway and such. The 50's lack of power was more evident out there. To make a long story short, Oct '02 we bought him an 80. If you'll be riding limited use in sand, the 50 will probably work. I have heard of some issues that the Cayman runs hot in the sand, but have not had much experience firsthand. Just my .02's.... hope this helps.
Ken
'01 400EX -- JE 426, HOT CAMS STAGE 2, 39 FCR, WB REV BOX, LRD PIPE, HINSON CLUTCH BASKET, +2" LT HOUSER A-ARMS, +1" HOUSER STEM, +1.25" HOUSER S/A, X-33 AXLE, REAR DURABLUE HUBS AND CARRIER BEARING, NO-PRELOAD ELKA SHOCKS, FULLBORE PLASTICS.