Once again a schedule change now has us arriving in JFK at 755pm connecting to an international flight to PSA at 850pm. Is that even doable?

If your in coming plane is on time, then yes. Not a problem.

JFK and all NY area airports have experienced very poor on time records. From where are you originating? Long haul flights into JFK tend to have a better record as they won't be ground held if they're coming from 4-5hrs away. Shorter flights - Chicago, Boston, East coast all are subject to ground holds at the departing airport if there are ATC delays in the NY area.

Personally, since you are on your way to Italy I would get an earlier arrival, even if it means hanging out at JFK for a long time.

For an international flight I'd rather be 5hrs early than 1min late.

55 minutes is more than enough to connect.

When you are connecting from domestic to international in US, you are basically just walking from 1 gate to another.

Assuming you are coming in on Delta and connecting to Delta, I wouldn't worry too much.

I would at JFK!

It's probably doable, but I'd be nervous. Like J62, I'd much rather spend a few extra hours at the airport than risk losing a minute of my vacation.