Would an extra 2" of tread width help?

I think the bigger tires will slow your 60 ft very slightly, compared to a GOOD hook with your current tire.
However, I think the extra height and width (both of which improve hook) will really help on your marginal track.
I'd spring for the bigger tire, unless you only want to run the track(s) with good prep.
As for how much? How "off" is it on the lousy track? Might lose .02 or 03 compared to good track, and improve by that much on the bad track.
(I ran a 14x32 on a 2500 lb ladder bar car with me in it, always hooked, best of 1.34/6.32)