I’ve gone to 75 minutes myself. Being a BIAB brewer with wide variations in mash thickness, that extra time has made my preboil efficiencies more consistent. I was seeing 5-8% differences in efficiency between my high and low-gravity beers with a 60 minute mash. Going up to 75 minutes brought my preboil efficiencies to the 80-82% range across the board. It makes life easier for me if I can simply follow one procedure for all my brews and get consistent results.
I think I am moving to a 90 min mash to see if I get an improvement for a few reasons: 1) One of the best beers I’ve brewed was because I ran out of propane while heating sparge water and had to run out for a fill. The result was a 90 min mash. 2) I often get lower than expected gravity points on first running and higher than expected on second running (batch sparge). Folks here suggested this is due to under conversion in the 60 min mash. This is probably due to my tap water being outside an optimum range because I know the temp and time. (I plan to get my water tested soon.)
We can definitely design a beer around a more fermentable wort. It just takes a brew or two to dial in the proper bittering balance. Underattenuated beers are one of the primary faults I find when judging homebrews. While having a thick and chewy beer can be satisfying, I find those beers are rarely enjoyable to the bottom of the glass or for a second glass. Having enough body along with an appropriately crisp or dry finish seems to create beers that can merit a second or third glass.
One thing that I’ve adopted from Mike McDole is to include a very small percentage of flaked wheat in my grists to enhance the body and mouthfeel of my beers. It works very well for me. Nice rocky heads.