Core Frequency: 335 MHz
Core Frequency Range: 255-378 MHz
Do I understand this correctly if I conclude that one chip will mine @ 335MH/s ? or 378MH/s if it's a good one ?
Yes.
255-378 MHz is the result of the back-end simulation under 1.2V. If you do an over-voltage, it will probably be significantly higher, but the stability is hard to say. Exactly how high a frequency we could push them to, could only be answered when the chips are out.
I think there is confusion between MH/s (mega hash per second) with MHz (mega hertz, clock frequency).