Hasta La Motion!

Hi guys i am about to purchase my first Mac just because of FCP. i am editor/designer by trade and i would like to know FCP and its lovely apple color correction. i will be using this machine for color correction and rendering with programs such as Cinema 4d After effects and some real flow.

I will be mostly editing in HD and HDV. Should i go with Imac or mac pro. The only reason i am thinking Imac is because of the screen since i cant afford color correction monitors closes thing would be imac screen since is HD. All 3 machines are refurbished from apple store here at my town. How safe is to buy refurbished are those machines older then the new Mac pro how can i tell if ti is 2 year model? How long can machine like this last me before it becomes absolute? Is there major difrance in DDR2 and DDR3

Any advice would help
Thanks guys

Here are my choices what do you guys think.
Mac Pro 2.26GHz 8-Core Intel Xeon

Two 2.26GHz Quad-Core Intel Xeon "Nehalem" processors
6GB (6x1GB) of 1066MHz DDR3 ECC memory
640GB Serial ATA 3Gb/s 7200 rpm
18x SuperDrive (DVD±R DL/DVD±RW/CD-RW)
NVIDIA GeForce GT 120 with 512MB GDDR3 memory
Mac Pro 8-core 3.0GHz Intel Xeon

Two 3.0GHz Quad-Core Intel Xeon processors
2GB (2 x 1GB) of 800MHz DDR2 ECC fully buffered DIMM
320GB Serial ATA 3Gb/s 7200-rpm hard drive
16x SuperDrive (DVD±R DL/DVD±RW/CD-RW)
ATI Radeon HD 2600 XT 256MB (two dual-link DVI ports)

iMac 27-inch 2.8GHz Quad-Core Intel Core i7

27-inch LED-backlit glossy widescreen display
4GB memory
1TB hard drive
8x SuperDrive (DVD±R DL/DVD±RW/CD-RW)
ATI Radeon HD 4850 graphics with 512MB memory
Built-in iSight camera