Assembly code: even less than that. I would estimate that all the assembly code, required by efficient SSL implementation, my fit between 100 and 500 lines of assembly, just one week/man project. Just smart man.
My own past experience tells, that when you insert efficient assembly fragments into C code, you can get 30% speed boost for the first 100 lines and then maybe 5% for another 100 lines and then 1% for even more 100 lines.