I have recently got into speed running the game and though I do understand that digital is faster than physical, is there a difference in running patch 1.2.0+ as opposed to older patches? I just wish to know whether it is a massive difference or worth me resetting the patch of my game (I also shiny hunt on the same game with a different account so don't know whether that would be hindered)

The current patch (1.2.0+) has extra lag when you enter your item bag in battle, as well as longer loads in a few other places. Overall it's slower, though the exact amount slower isn't exactly known yet

Also, you can't reset the patch. You're stuck on 1.2.0+

(well, physical can technically downgrade, but it requires factory resetting the switch and never connecting to the internet ever again on that switch)