If you can donate it to SCI later, the value of that donation gives a lower bound. You also might be able to donate to something else you find.
I misread your earlier comment, sorry for the useless response. I understand where you're coming from now. Holden has written about the possibility of efficient opportunities for donors drying up as the philanthropic sector improves, suggesting that it might be best to help now because the poor people who can be easily helped are around today and will not be in the future. See this mailing list post.
I personally think that even if this is true probably true, the expected value of waiting to give later is higher than the expected value of donating to AMF o...
As of today, GiveWell has two new top charities:
1. Against Malaria Foundation
2. Schistosomiastis Control Initiative
Their previous top charity, Village Reach, no longer has much room for more funding. Which is a good thing: partly through givewell's influence they now have as much money as they can put to good use.