Leo I know you were basing it off some type of freestyle riding, perhaps I worded my response wrong. What I was getting at is that size wise if he's more interested in riding a lot of park..especially with a lot of presses, jibbing, butters he might enjoy the flex of the 154 more, its certainly still going to be plenty stable for him. If he is more interested in bigger jumps and charging harder, the 157 might be the call. I wasn't suggesting the Proto as a big mountain ride like a premier would be.
Size wise I'm pretty close to his weight, I'm 155lbs, and the 157cm was challenging to press and butter well. I enjoyed charging on it though. My everyday ride a 155 cm. evo but I will be downsizing to the 152cm proto for next season...just my $.02.
If you get a chance to ride an SL I think you'd be into it. Its a SUPER fun board. I would be all over it but I prefer riding twins.