Need some help deciding

I need some help picking a new computer. I do some moderate gaming (L4D, Warhammer) and I'll also be doing some CAD'ing once school starts. I don't want to spend the time building a rig myself so I'm looking at to options from HP.

1. HP Pavilion Elite e9150t

Intel(R) Core(TM) i7-920 processor
6GB DDR3-1066MHz SDRAM [3 DIMMs] from 4GB
640GB 7200 rpm SATA 3Gb/s hard drive
512MB ATI Radeon HD 4350 [DVI, HDMI, VGA adapter]

PRICE: $765

2. HP Pavilion p6180t

Intel(R) Core(TM) 2 Quad processor Q8400
6GB DDR3-1066MHz SDRAM [4 DIMMs]
FREE UPGRADE! 640GB 7200 rpm SATA 3Gb/s hard drive from 500GB
Integrated graphics - Intel(R) Graphics Media Accelerator X4500 [VGA]

PRICE: $577

I will be upgrading the graphics card in either one so basically it comes down to the processor. Is the extra $200 worth the upgrade from the Q8400 to the i7-920?

Also, how are HP's when it comes to noise level, temperature, etc.