Plus, if there is an "global optimal max size", it's quite pretentious to claim you can come up with the "optimal formula" to calculate it. Even if you could, individual peers would never have all necessary data to feed to this formula, as it would have to take into consideration the hardware resources of all miners and the network as a whole. That's impracticable. Such maximum size must be established via a decentralized/spontaneous order. It's pretty much like economical central planning versus free markets actually.
I think that if we reach the 1mb limit and don't upgrade with a solution, then the spontaneous order will create fiat currencies backed with bitcoins, in order to reduce the amount of transactions in the bitcoin network. So, this would also lead to less revenues for the miners (plus a loss on reputation for the bitcoin network).
The block size hard limit is nothing but a protectionist policy.
Even when misterbigg's approach might not be the optimal solution, at least it's an idea.