I believe you would be looking at a pair of 4870 x2's, in that case.
As far as power consumption, the number that pops in my head is 260 watts under load. Though I may well be completely wrong on that, and will shortly suffer gleeful correction on that at the hands of someone else.
So, 260 watts x 2, plus whatever else you need for the rest of the comp.
Personally, I'm one of those a$$holes who figure out their actual 'needs', then doubles that. And I also believe in buyng top tier components. So if you're looking to save some cash, I'd be a pretty poor reference.
Technically, a card backwards-compatible with PCI-express 1.0 that has a 6-pin plus an 8-pin connector theoretically cannot exceed 250 watts of consumption, since a x16 PCI-e 1.0 slot and a 6-pin connector can only provide 75 watts of 12v current each, and the 8-pin one 100 watts.
But yeah, it'd still be high. To be certain, I wouldn't get anything less than an 800w or so PSU; you want some leeway so that fluctuations in current won't hurt you so much, and so that it doesn't burn out by having to run at close to 100% all the time. And of course, because you'd actually be using anything remotely CLOSE to its actual rated capacity, make darn sure it's a good-quality unit.
Are there any Quad PCI-Express motherboards that support 2.0 and are Crossfire to use 4 Radeon 4870 X2, and with a Intel 9450 CPU and about how much power would that consume. Would a Thermaltake Toughpower 1200 Watt PSU that is Crossfire certified power-supply be the option?
Thermaltake is a rather good brand, and anything that's 1kW or higher should provide sufficient juice to run pretty much any rig you can plug it into.
And as a note, there technically aren't any motherboards capable of using four PCI-express slots together at once; there is a motherboard or two that has four slots, but they can only be used to drive separate displays. Quad CrossFire and Quad SLi rely on using a pair of dual-GPU boards, like the 4870X2.