I upgraded my MacBook6,1 MC207LL/A system which has the 2.26 GHz P7550 and the MB61.00C8.B00 boot ROM today with 2x4GB 1333MHz (Corsair CMSO8GX3M2A1333C9) and it is indicating the RAM is 1333 MHz and I haven't encountered any issues yet. Update: Although the system was stable, it did seem to be running quite hot. I didn't spend enough time using it before upgrading the RAM to know if this was due to the RAM or not. I went ahead anyway and underclocked the RAM to 1066 MHz by modifying the SPD of one of the sticks using i2cdump and i2cset in an Ubuntu install on a USB stick.
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