ive heard the optimum weight for a radial at about 140.... def dont wanna be over 150 tho... i guess you could do it but it would be painful in light air. it seems like too big of a gap though, b/c you're not going to be that competitive in a fullrig until 165-170. I guess you just dont want to be in the 155-165 range. too bad b/c thats what a lot of teenage guys would be.
It depends alot on the wind strength as well. If I'm just out having a good time I find that in heavy wind I can maintain much better control with a radial than a full rig. Consquestly providing me with the ability go faster instead of fight the boat for control. 8)
See the PSE's (UK and Europe manufacturer's) site (www.lasersailing.com) for ideal crew weights. Select boats, then laser, then 4.7 and find the "tech spec" section. The figures are in kilos: 2.2lbs = 1kg. This will give a sailing weight not a racing weight so add a bit to the lower end of the range for the ideal racing weight but you should be able to handle a 4.7 at the weights specified.