As long as SBD creation rate remains the same, a higher rate on it will not change much.
A higher rate also means that more SBD will have to be created just to sustain the rate, even if all author rewards dropped to zero.
Since you probably want to leave SBD creation rate as it is, a 50%/50% rewards choice with less SBDs and then the power up 100% will also mean less STEEM for authors, since it has to be worth the same, aside from SBD fluctuations compared to USD, and it all means more STEEM for witnesses (?)
You just led me to realize that over time, Steem's witnesses will take more and more for themselves on the expense of the authors, and make it even less beneficial to post, and it is already not beneficial to post here, unless one combines it with other platforms.
Only big authors with a lot of vested Steem and some functioning thought process might prevent it, and my bet is that it will not be prevented.

There is already a higher rate on STEEM (rise in STEEM price of vests) and this is one of the biggest reasons for the down trend of STEEM price.

It took me some time to post as well as multiple corrections and a visit at the toilet to think about it, and it probably still requires some corrections and additions and may lead me to new realizations.