How many "primespersec" are you guys getting? I have an i7-2700k and it is fluctuating between 20 and 120 primespersec for me.
Steady 100 primes per sec for me on an i5 @ 4.4 GHz
help -> debug window -> console tab
type setgenerate true -1 in the bottom text field and hit enter. (this enables mining on all CPU cores)
Now if you do a "getmininginfo" in that same window, you should start to see your primespersec reported.