They look similar but there is a difference. The 1N5817 is rated at 20V, with a 450 mV drop at 1A and the 1N5819 is 40V, with a 600 mV drop at 1A. This makes the 1n5819 slightly inferior to the 1n5817.
Also to get the required voltage out you would need to make about 2% more voltage in at the same current with the 1n5819.
I would stick with the 1n5817.
yes, as urbanghost mentioned the best option is the 1N5817.
We need the Vf to be as low as possible, with the 1N5817(Fig.2 in the
1N5817/1N5819 datasheet
) the VF at low currents, lets say 20mA, is always below 0.25V which is great. In the 1N5819 is always 0.5 which is not enough.
The only constrain for this diode is to have a VF below 0.3 at low currents.
