I honestly cannot reproduce lag issues. But, there is a good chance for whatever reason this new driver isn't working without libvalidation fixes. 10.13 drivers haven't required nvidialibvalfix to fix windowserver acceleration before, but it might require it now. I've always had it because I constantly mod driver, and, if you do that, then you DEFINITELY need libval fix.
I've been using safari all night and day today, watching twitch and YouTube and seen no lag anywhere with driver. The ui sluggishness and beach balls described sounds exactly like what would happen if Windows server wasn't accelerated do to failed library validation.