That is powerful enough, I have the non modular version of that. The only problem is it only has 2 PCI-E 6 pin connectors so you will have to use adapters for another 2 connectors. I remember a while back a review where they ran 2 8800GTX's in SLI with that PSU so it's powerful enough.
I am planning on Crossfire when the 1gb 4870's are released and I was trying to decide if I would be better off selling my PSU and getting something with 4 PCI-E connectors or just using adapters and I still haven't decided yet. If you decide to use adapters just make sure they are on different rails, the PSU has 4 rails 1 for motherboard, 1 for PCI-E, I believe 1 for the molex connectors and 1 for the SATA connectors.