My first response would be YES, since the time difference between the JFK-GRU flight and ATL-GRU flight is exactly 30 minutes now. More importantly, because between immigration and the taxi queue, I spend 1+ extra hour standing, tired and warm at GRU.

I looked at the Delta flights again to confirm:

If you fly now, the flights are as follows:
ATL-GRU: DL105 7:30p-6:10am
JFK-GRU: DL121 9:45p-8:50am

After March 26 the Flights are as follows:
ATL-GRU: DL105 9:40p-8:15am
JFK-GRU: DL121 9:55p-9:00am

So the flight duration are ~30 minutes difference. The the arrival time is drastically different. In both cases, the ATL flight arrive sooner, so logically, your wait time at the airport is less.

For someone from LAX, the connection time may dictate which flight you take. I guess it would be pretty brutal for a westcoast person to get up at 6:10am Brazil time and go through immigration in Brazil...

BTW, I also looked quickly at orbitz and found there are multiple flights from AA and United landing in GRU from JFK ~8:30am, so with your 9am arrival, you may have to wait extra long.....

Someone who has taken the JFK-GRU flight comment on wait time?