With 17k for the 8 core 2.92 numbers being so high, it doesn't take a lot to extrapolate some results from those to guess what the four-core nehalem is going to be like:
2.92 x 8 = 17665 geekbench
If that scales perfectly with 100% utilization of all cores, the base model 4-core would be:
17665/2.92/2*2.66= 8046 geekbench
This puts it just under the 2008 2.8 eight-core which isn't bad for a four core entry level Mac Pro.
More realistically, the second chip on the 2.92 is likely to be underutilized compared to the first, with diminishing returns as shown by the 6x results from the cinebench test. I'm guessing the four-core machine pulls at least an additional 15%, putting the GB around 9200, pretty much a dead heat with the 8-core 2008 model.
This creates a bit of a quandary for the new buyer. 8 core xeon 54xx on liquidation or four core nehalem? Applications that don't take advantage of the second cpu may prefer the nehalem system, and the GT120 is a better video card that the stock 2600 that comes with the 2008 model.
I think it will all come down to RAM and specific application performance. Personally, I'd love to see some Handbrake encode numbers from the 2.66 Nehalem....