I think there is still a difference because of the calculations. SBD is always calculated as if it is worth $1, even when it is above or below that amount. But if you choose SP, you don't get anything calculated as SBD.

So even if you get paid in STEEM and SP I think the calculation is the same. You are just given STEEM instead of SBD. But if you get the payout as all SP, then SBD at $1 is not a part of the calculation.

I know that when SBD was above $1 I was getting more total reward by choosing the 50-50 split. I've assumed since SBD fell below $1 that the reverse is true. Since I always power up anyway, I haven't bothered to work out the numbers and be sure though.