Thanks everyone. I guess I revealed the date already. Every other Saturday night from EWR (for several weeks before and after) it's a 738/739, but I'm stuck with that day with the choice of A320.
I didn't know before I first posted, but have since learned more: An upgrade on the A320 is merely 2 inches wider and longer, while Y on the 757 p.s. means personal TV and power plug (wifi is worth a lot less when you run out during a long transcon).