Clock for clock it would be tough to give a definite winner.
The E6320 is based off the older Allendale core.
While this revision of the microarch is about 5% slower than the E3300's Wolfdale 3M arch, it does sport more active L2 cache.
The best I could offer between the two is that, clock for clock, it would really depend on the application as to which is faster (and neither would be faster by much).
The E3300 is a better CPU because it is based on the Wolfdale 3M microarch, newer and more overclockable 45nm process and has a higher multiplier.
Assuming you have a decent chip (most are), you should have no issues getting it well past 3Ghz.