I don't whant to ask stupid questions, but....
the 5870 usually has a clock/memory speed of 1200/850.
Do you realy slow down the memory to like 300 MHz?
And you also slow down the clock to like 900 MHz?
I'm waiting for my own 5870 and I thought it be good to slow down memory to reduce heat production and therefore tune up the clock?!
The memory is not so important, right?
your numbers are switched, the memory clocks are always higher since I can remember, but yes, you overclock your core and underclock your memory...