Overclocking RB1100AHx2 to 1500MHz

In http://forum.mikrotik.com/t/rb1100ah-new-product/44731/20 MT stated that the maximum frequency of the CPU inside RB1100AHx2 is 1500MHz, despite this board is shipped by default at 1066MHz.

However, if I try setting:

[admin@MikroTik] > /system routerboard settings set cpu-frequency=1500MHz

it seems that 1500 is not an accepted parameters. Why?

I managed to set it to 1333MHz.

Thanks

Deleted because not related.

RouterBOOT is limiting the available options so that you don’t burn the CPU