Thanks everyone. Some very mixed views on here.
According to eXtreme PSU Calculator my setup will only use 451W at full load (Assumes no overclocking)
I'm not convinced by this.

The 600W power supply will at least take the 7950 on it's own.

I'm tempted to put the 6850 in but not mine on it for now. what do people think?

I would like to get another 7950 at some point and would need a new PSU anyway, what would you all recommend for the PSU?