I find it difficult with the current reward system to make money as a curator and beat the built in inflation of Steem. So 50/50 would be good.
Another way for whales who like to do manual curation and support quality content would be to approach an author they want to support on a more regular basis because the author produces quality content, tell the author to put their post reward on 50% power up and after he got the reward for a certain post the author transfers the SBD part of the reward he got from the whale back to the whale´s account. That requires a bit of work, calculations and some initial trust by the whale but if the author does not transfer the SBD he looses all potential upvotes by this whale in the future, so it is in his best interest to pay the SBD to the whale.
Compared to vote buying where the minnow has to pay SBD first and is restricted by his lack of capital or some limits imposed by the bot, here the whale and the minnow could agree on an individual contract involving bigger upvotes.
This could maybe also be an alternative for whales to the opening of several accounts, publishing crap content and then upvoting those posts to keep all the rewards for themselves, because as @starkerz said at steemfest in the long run the whales interests should be in increasing the value of Steem by promoting steemit and not some petty curation rewards.