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?