Considering how the S4 Pro in the Nexus 7 is actually just a downclocked version of the Snapdragon 600 I presume there is a decent amount of wiggle room for overclocking. Yes, these are probably the worse chips out of the binning process to have been condemned to live the rest of their lives as S4 Pros, but would hope all of these should easily be able to achieve the 1.7Ghz Snapdragon 600 specs. Maybe even some lucky owners could push theirs to and beyond what we see in the Galaxy S4 at 1.9Ghz.
Now I'm just speculating as my Nexus 7 isn't even here yet (still in shipping). I made this post to make some discussion on the matter. Like people who've already tried messing with clock speeds and voltages on theirs could share their findings here. Talk about what kernels permit what levels of tweaking. Or even GPU overclocking/governor tweaking etc...