they also usually have teams in that 5-8 range that would benefit from an expansion.

Based on the last 6 years, the main conferences that would be HURT by the playoff would be the SEC and ACC. SEC dominates the current format and expanding would only bring the Big 10 and Big 12 on par with them as far as bids.

ACC is hurt because Clemson always seems to get a bid and would have a tougher oath to a title in am expanded playoff. However, you could argue that an expanded playoff would remove the scenario of them being left out for losing a single conference game along the way.

Big Ten, Big 12, and PAC-12 all would stand to benefit form an expansion of the playoffs, though.