The thing is, you have chosen this line of reasoning (however sound it may be in general application) to explain Ben Spies performance difference from world superbike. conventional wisdom/observation skills will tell you that Ben is not as good as the top end motogp riders yet, you may also recall how other superbike riders have expressed the relentless speed in motogp right from the word go, and how that is difficult to adapt too. Additionally Lex quite rightly pointed out Ben's equipment could be a factor. It has also been mentioned that Ben shows no signs of fatigue or tiring, is fit enough to be a hugely competitive cyclist, and that his weight has not changed significantly since the times when this problem certainly didn't exist. Yet despite all of this, you assure us all that Ben, his doctors, physical trainers and diet experts have simply overlooked something that is relatively common knowledge (apparently).
Even if he does suffer from the issue you describe, who's to say he'd be any faster by putting on weight to increase his mental capacity. Maybe he's already struck the best possible balance. I don't know if you are some kind of die hard Spies fan trying to justify why he isn't as good as you had hoped he'd be, but your explanation is pretty far out, and i think at least Ben is doing a pretty decent job in motogp so far.
