Not exact comparison, but I replaced my Acme 537 (13.5x16) with the Acme 2079 (14.5x12) on my 2001 X30. I love it. Would even say that it completely transformed my boat's performance and enjoyment, but don't want to be overly dramatic. Considered the 15x12 but was going to be a bit tight, and figured 14.5x12 was already a huge change for me.
Your two questions: Fuel burn- i burn less gas now (my 537 cavitated slightly when surfing, increasing fuel burn), Plane time- not even a fair fight in my case, 12er hole shot is ridiculous and planes very, very quickly.
We surf most of the time so fully loaded with 3000# plus crew. The 537 would cavitate badly with that much load, so I could only run about 2000#. The 2079 pushes 3000# effortlessly. In addition, oddly, my RPMs at 11 mph went DOWN compared to the 537. That tells me the 537 was cavitating some even with the 2000#, just not bad enough to notice (yikes !).
Wakeboard with way less load, so 537 was fine, but 2079 hole shot and plane time is way better. Certainly no downsides using 2079 for boarding.
WOT went from roughly 38mph/4800 rpm to 35mph/5000 rpm, but we never run it like that. Even when cruising we stick around 25-30 mph.
For me, it was "finesse" versus "raw power". Used to be "hit it" to yank the boat out of the water and wait (hope) for it to plan, now we just ease into it even with full load. World's Strongest Man, when the huge guys pull a tractor trailer: that is how I feel about my X30 now with the 2079.