It's a more complex question than you or most truly realize. It depends on the MOBO, I mentioned the RAM limitations but some non-P67/Z68 can limit the Turbo-Boost but some Z68 have slower USB and SATA speeds in comparisons to other LGA 1155 MOBOs.
So the only answer is 'Yes, No and Maybe' depending on which speeds, on e.g. 'Turbo' non-K SB CPU alone then even the non-K will benefit from P67/Z68.
Here's a good video that explains some chipset differences: