Thanks everyone for the great advice and observations.

What complicates this a bit is that I'm flying to SFO from LAX the prior evening. The D1 fares from LAX-EZE were about double what was charged for SFO-EZE. I'm spending the night at the Grand Hyatt so it's an easy ride to the terminal but 6am is still super-early. My leaning to the original JFK flight was the lay-flat SFO-JFK (757) so that I could just catch up on sleep while heading to JFK. Even an 8am departure would mean I'd still want to sleep and a standard domestic first class seat isn't really conducive to that for me.