Thanks to authorized Mac dealer B&H Photo, a 4-core 3.5 GHz Mac Pro is arriving at MPG for testing next week.
Note that B&H Photo has substantial savings on AppleCare versus the Apple price.
This is the base model, the least expensive and it ought to make an excellent reference for all the other models. See the test results for the 2013 Mac Pro. In particular, how does a fast 4-core CPU stack up, and how well do the D300 GPUs perform on GPU-intensive tasks?