We will just have to wait until the real specs for the card is released, like PSU requirements. You may or may cut it with that PSU.
Better yet, skip that case entirely and go for a case and a good PSU.
I'd recommend a $70 Antec Three Hundred Case which will house 10.5" GPU's like the GTX 280 without eating into the hard drive case, although to remove the hard drive, you'd have to remove the GPU first if it's the 10.5" variety (longest cards). Other 2 HHD slots are fine. Then throw in a good Antec/Corsair/PCP&C PSU and you are set.
nVidia recommends a minimum 500W PSU for systems with a GTX 260. Of course, if you have a quad CPU in there and more than 1 disk and more than 1 fan and so on you probably want more than the minimum recommended PSU. Also, PSU efficiency tends to be best around 40%..70% of the PSU's range, which means it's better to have a big PSU used at, say, 60% of its max than a smaller PSU used at 90%.
Edit: LOL, you found that link on nVidia's site at the same time as me
NVIDIA SLI®-ready1 2-/3-way
NVIDIA PureVideo® Technology2 HD
NVIDIA CUDA™ Technology
Microsoft DirectX 10
Bus Support PCI-E 2.0 x16
Certified for Windows Vista
Maximum Digital Resolution 2560 X 1600
Maximum VGA Resolution 2048 X 1536
Standard Display Connectors 2 dual-link DVI and 1 analog HDTV-out
Multi Monitor (# of displays) 2
HDMI6 Via Adapter
Audio Input for HDMI SPDIF
It should fit in the RC-690 all right. Even the 8800GTX fits in that case, and it's almost 11" long. You can put even two of them in there.
The Sonata 3 also can fit an 8800GTX, so it should fit the GTX 260 too.
However, I'd still prefer the RC-690 for a gaming machine because it has 3 fans (and room for 4 more), while the Sonata has just one. Don't get me wrong, I love the Sonata 3, I have one at work right now, it's just that it's not designed for systems with high-end video cards that dissipate a lot of heat.