[quote] Were the batches otherwise identical?
[/quote]
Yes, they were. I’ve thought about going back to fly sparging, for the reasons you mentioned, but batch sparging is just less trouble with my setup.
Sure, a 170°F “mashout” can improve efficiency if you haven’t reached 100% conversion, but it doesn’t seem to matter if you’ve already achieved 100% conversion at the end of the sparge.
I have pretty much adopted a mash temperature sparge routine and get around the maximum lauter efficiency mathematically possible for the volumes that I use. I get the same for a 170°F sparge. I can’t really speak to very high gravity beers, where you might expect to see more effect on viscosity, but for normal gravity beers any effect of high temperature is apparently on pushing saccharification to completion.
The difference is in getting higher efficiency by improving conversion or by sparging more stringently, which risks adverse effects on flavor.
Mash, batch sparge, boil.
Ain’t got time for the details.
Amen…Except, I double batch sparge.
Then you’re wasting time that could be spent on something like drinking! 
I don’t mash out anymore(thanks to advice from this forum) and I haven’t seen any decrease in efficiency.
I’ve never mashed out. It’s difficult when your mash tun is a cooler. The only way to raise the temp is to add more hot water.
Not mashing out has never seemed to be a problem for me. I’ll have to try batch sparging at some point, though, see how much time I can save in my brew day. 
Not the only way. If you really want to do a mashout, you can draw off some wort, heat it to a boil and add that back. I never use decoctions to add flavor, but I often use them (without an etended boil) to raise the temperature of my mash.
True… but I just don’t bother.
When I read the OP the first thing I thought was that after a 90 min mash @ 150* F, a mash-out wouldn’t make that much difference. I often mash for much shorter times (like 45 min but only when mashing at higher temps) and in that case I see a fementability difference…no mash-out = more fermentability for that given mash. I fly-sparge…if at all.
Recently I’ve been reducing my sparge volume more and more (to the point of no-sparge) and surprisingly have not suffered much loss in efficiency. So these days I’m mashing REALLY thin and only sparging a gallon or two and still getting ~73% brewhouse efficiency. I had it up to 92% at one point but intentionally dialed it back, there were a few over-sparged batches in there.
I always do a mash out and I never have a stuck sparge. Whether it really helps or not doesn’t really matter to me, because I’m not playing with success.
Another question would be why mash out?? Unless you are trying to create exactly the same beer every single time, seems like an unnecessary step. I’ll get that wort up to 170 in no time in the kettle!
I read that the increase in temp for the mash out is to lower the viscosity of your liquid so you get a better flow during sparge…and this makes sense as it would give a better rinse to your grains.
That’s always been my experience. I haven’t had a stuck sparge in years.
It may make sense, but it’s been proven to not actually make that difference.