The 2620 would be better. Though clocked lower, you have 50% more L1 cache, as well as 2 extra cores which will more than make up for the lower clock speed
idk about the cache difference, but if they scale properly then wouldn't the 4 be better? 4*3.6=14.4 while 6*2=12, so the performance would be better even with a six thread application, although idk if those are hyperthreaded or how that would affect the performance at that speed.