There are a few things off with that your screeny that i can see other than it reading the core at 420, also no validation
-The score... 139 points - a 460 at 760mhz core on that open gl 2.0 benchy gets around 2400 points
LINK and my 580 gets 4000 UNDER clocked a bunch.
-FPS 3 min 4 max 3 avg - seems way to low considering my 580 gets 75 min 90 max 83 avg again UNDER clocked
-max temp 39c?
id re run it at stock and see if your score improves cause i wouldnt trust that score for a stable clock at all