The Oculus store has a 30 day return window now so it may not make much difference anymore imho.
As far as IPD goes, mine measured recently by my optometrist is 69.0mm. I can’t really see any difference with +/-2-3mm with either my Rift cv1 or Quest 1.
I also have a Go with fixed 63.5mm and I have never had any problems or eye strain even watching +2hr movies. Could be that my +60yo eyes are more IPD tolerant. Apparently persons younger that 30yo are more sensitive to this. Whether or not you wear glasses with the headset may also make a difference. Who knows?
in any case I’m confident that the 68mm Quest 2 setting will work fine for me. I’m more concerned about losing those nice Oled blacks/contrast in dark games. Guess I’ll find out in about 4 weeks time!