I'm going to disagree (sort of). We already know from the Apple site that it's a single core machine and it will have "up to 12 cores of processing power." We also know that on September 27th, Geekbench reported scores from what they claimed were a legitimate 8 core machine. The current Mac Pro has a 4 core base with a 6 and 12 core upgrade.
You have several flawed notions going here.
1. It is single CPU package ( not core). The Xeon E5 models that are designed for single package systems are the E5 1600 series. Apple is probably going with the newest ones so that E5 1600 v2 ( "Ivy Bridge).
Those models come in 4-6 core configurations.
http://www.cpu-world.com/news_2013/..._E5-1600_v2_and_E5-2600_v2_CPUs_launched.html
Apple will use some E5 2600 v2 processor packages also ( it is only way to 12 cores) but those will be far, far, far above the entry level configuration price points. Apples first two configurations in 2009-2012 used around $300-600 processors. If aiming at the same price points they likely still use exactly that price range for components in this 2013 Mac Pro.
2. The E5 1680v2 that "leaked" in benchmarks isn't just north of $1,000, it is pretty close to $2k ( $1723).
http://ark.intel.com/products/77912/Intel-Xeon-Processor-E5-1680-v2-25M-Cache-3_00-GHz
By the time Apple adds their 30% mark-up that will be about $2,239. That is just for the CPU package itself! The completed system with RAM, 2 GPUs , etc is likely in the $4-5K range for that configuration.
The fact that the iMac is a quad core machine I think Apple will want to put more perceived separation between the two desktops.
There are more to these systems than just CPU cores. The Mac Pro will have two GPUs (likely midrange and fully clocked ). The iMac typically has mobile GPU and even top end GPU is a significantly underclocked desktop GPU. The Mac Pro has 6 Thunderbolt v2 sockets. The iMac 2 "last generation" Thunderbolt sockets. The Mac Pro has SSD by default. The iMac nominally has a HDD. The Mac Pro's E5 has twice as much memory bandwidth (and twice as many memory channels ). The iMac has two.
On "horsepower" , multiple core, workloads the 4 core E5 1620 v2 will be highly competitive with anything the iMac can bring to the table. It is only on single core drag racing benchmarks/apps that there will be an edge for the top end iMac BTO option.
In short, they
are differentiated.