> With higher frequencies ( 1.4 GHz and above ) I had memory read errors.
> From my opinion is northbridge MV64361 responsible for this, not CPU.

The northbridge being responsible for this doesn't seem plausible to me. The northbridge does not care for the CPU clock rate at all. It runs at the same clock rate no matter the CPU clock rate.

> the max frequency is 1.464 GHz

Is it a given that 11x is the highest possible multiplier? After all, the 5 binary digits of the PLL config can theoretically represent 32 different numbers, and with 0.5 steps this could amount to a 2.07 GHz range.