This is caused by the fact that they are the same chip.
6650M = 6750M except that 6650M has DDR3 video memory with 6750M has GDDR5 memory. I'm not sure if there is a reliable way to tell them apart.
I'll report this and we'll see if we can somehow separate them. In any case the performance estimation is probably fairly close as currently it is based on an average of all 6650M/6750M benchmark results.