I have a Corsair AX850 Professional Series GOLD certified PSU...
ATI Radeon 6850 in Crossfire
1x 500GB Seagate Barracuda HDD, 1x 1.5TB Seagate Barracuda HDD
4GB of 1600MHz DDR3 Corsair RAM
Intel Core i5 650 3.2GHz OC'd to 4.0GHz
Asus P7P55D motherboard
Four or five chassis fans
I would estimate your current setup using 430-500 watts. Even overclocked. Your PSU should be more than enough. So it should hold out for the life of the system unless you upgrade the video cards to 6970's... which would put you around 700-780 watts estimated power. The same PSU would still be enough though. Just closer to the top end of the PSU's continuous power ratings.
I've seen three way SLi on an certified 850w so yes your PSU is enough, you still have about 300w free so you're fine.