According to Positron (in this post) an nVidia 9800 GT would be sufficient as of the time he posted. Two 9600 SLI'd together? Probably. (Keep in mind, things may change depending on exactly what goes into Ultra mode, how they code it, etc.)
Offhand, I can't find a post by a redname where they've said what minimum processor and RAM you'd want to have. (The linked thread is entirely about graphics cards, so, sorry.)
What will be the minimum system requirements and the recomended system requirements for Going Rogue. Especially in order to have Ultra Mode turn on
I have AMD64 X2 4600+
4Gigs Ram
2 NVidia 9600GTs SLI'ed together
Will that be enough for Ultra Mode?