This is basically the same as https://bugs.webkit.org/show_bug.cgi?id=240605 . Safari and Chrome can run pretty close to the max complexity of multiply. This leads to a lot of variability in the scores.
Pull request: https://github.com/WebKit/WebKit/pull/15849
<rdar://problem/112664646>
I've done some local testing and I think we need to bump to 68 rows. Hopefully you won't mind if I take over the PR?
This is being fixed in https://github.com/WebKit/MotionMark.