From what I have been reading SBD should be about $1 worth of steem power however lately that price has dropped back down and is currently sitting at $0.90 for a SBD which I believe now signals you would earn more by doing power ups on your posts. If a SBD should be valued at over $1 again then your 50/50 split would pay out the most. The other thing to consider though is if you do a 100% power up it all goes into steem power which does take time to cash out if you should wish to.