Do note that A32x do have wider seats than 737's, 18" vs 17". It's enough to make a noticeable different in comfort for some of us. Now that I'm no longer chasing status, I actually prefer Jetstar for this reason on SYD-MEL* and similar routes and would be willing to give a longer A321 route a try. Qantas 787's are only about 17.5" inch wide so actually worse than the A32x. . I've done 757's for transatlantic and they're not brilliant, but really not that much different than any other longhaul flight especially in an aisle seat.
* Note that I refuse to fly MEL-SYD on Jetstar due to the insane madness that is MEL's T4 (for arrivals I can just walk through but departure is a mess.)