We're building performance tests in order to obtain some performance numbers so we can add them to the comparison chart, but will not publish them until the final product is released.
So ...unscientific is all we can provide at the moment. On my Dell Vostro 400, which is a <$1000 business desktop, I just ran the latest nightly build to check on the current state of affairs (for this post). I got the grid in table view running with 1,000 columns * 1,000,000 rows and scrolling at a framerate of about 2-5 times per second vertically, 2-3 times per second horizontally (column virtualization is turned on). If I try it with 100 columns * 100,000 rows, subjectively, scrolling framerates seem quite decent. I believe they are now faster than our Windows Forms grid, but haven't compared side-by-side yet. One thing to note though, is that there's a lot of stuff (virtualization, container recycling, garbage collection, other optimizations) going on under the hood, so unlike the Windows Forms datagrid, which scrolls at a uniform speed, the WPF datagrid speeds up / slows down at seemingly random intervals. At times the scrolling is amazing, at other times there are small lags. The average speed though, seems good. The 3D views are pretty fast too. Noticeably faster than the 2D carousel views I've seen from 3 competing products so far.
BTW, this all works with .NET 3.5, does not require .NET 3.5 SP1.
VP, R&D, Xceed