Just got my crystal oscillator circuit built and installed onto my block erupter.
Without changing the voltage I can get stable output with a 13.5mhz crystal

that is 378 mhz. averaging 350-360 mh/s
Still need to test more.

1 clock is 1 hash, so 378MHz should give almost 378mhash, minus errors.
I get 335.8 displayed in CGMiner with my stock sticks.
So there is something wrong with yours or you didn't wait long enough...
do your be's ever malfunction at start up? when i restart cgminer, AMU 0 reports 458 MH then it gradually steps down to 335.5 where it settles in a groove and fluctuates about +- .5 m/h. sometimes AMU 1 gets stuck at 400.29 m/h and then crashes and reads "ZOMBIE: 0.000 mh/s A:0 R: 0 HW: 19