Mac Pro: 2 dual core vs. 1 quad core processor - which is better?

Thanks for the lead on the refurb. That looks good. I checked out eBay and found something that caught my eye. I wonder how something like this compares with the new Mac Pro? (processor, memory, video card)

Processing

8-core: Two 2.8GHz Quad-Core Intel Xeon 5400 series processors
12MB of L2 cache per processor (each pair of cores shares 6MB)
1600MHz, 64-bit dual independent frontside buses


Memory

800MHz DDR2 ECC fully buffered DIMM (FB-DIMM) memory (CURRENTLY HAS 8 GB INSTALLED)
Eight FB-DIMM slots on two memory riser cards (four slots per card) supporting up to 32GB of main memory

Graphics

ATI Radeon HD 2600 XT with 256MB of GDDR3 memory and two dual-link DVI port

Communications

Two independent 10/100/1000BASE-T Ethernet (RJ-45) interfaces with support for jumbo frames
Bluetooth 2.0 + Enhanced Data Rate (EDR) up to 3Mb/s

Storage

Hard drive bay 1

1 TB RUNNING AT 7200 RPM

Hard drive bay 2

320 GB BRAND NEW
FOR A TOTAL OF = 1320 INSTALLED

I lost the auction on ebay for the above computer. It sold for $2,560 with shipping.

Looking at other ebay Mac Pro options, I came across an "April 2007" 2 x 2.66 GHz Dual-Core with 9 GB of RAM. Here are the specs:

Mac Pro Intel 2 x 2.66 GHz Dual-Core Intel Xeon 9GB
9GB RAM and a 250GB Hard Drive.
2 Nividia GeForce 7300 GTVideo Cards - runs 4 monitors
MacOS X clean installed -. 10.4.11
Comes with keyboard, mouse, power cord & original install disks included.
memory: 9 GB
hard drive: 250 GB
cd drive DVD+/-RW/CD-RW

operating system: Mac OS 10.4.11, Tiger
firewire: 4 ports
usb: 5 ports
video card 2 Nividia GeForce 7300 GTVideo Cards

I realize that it will need an OS upgrade to Snow Leopard, and I would also install a couple of 1 TB hard drives. Can this setup be recommended? I would hope that I could bring in all costs including the upgrades for under $2,000. Does this make sense? Are there other suggestions for changing out hardware, or would you recommend that I forget this as the basic computer is just too out of date?

Thank you.