best PC specs for HD video capture?

[clashradio]

Hello,

I currently have a PC used for general video work (standard def, some HD as well), some audio work, internet, scanning pictures etc. Looking to upgrade for HD capturing & workflow. My current set-up drops frames, locks up, seems like it's not able to handle HD captures.

Current specs are:

PC: Windows 7/64 Ultimate
MOBO: Asus P8Z68-V ProGen 3 (with usb 3.0) i7-2600 CPU @3.4ghz RAM 16G
Graphics Card: Nvidia GeForce GTX 560Ti
Sound Card: Scarlett 18i6
card reader: Koutech (w/usb 3.0)
Hard Drives: (1) 500G for programs (2) 6TB for workflow (these drives are independant; not raided, mirrored or stripped and are brand new)
NLE program: Sony Vegas Pro 12
Capture device: Blackmagic Intensity Shuttle usb 3.0


Does an internal PCI/e card capture better/faster than an external usb 3.0 device?
I've been told Asus is not the best mobo out there
Hard drive configuration have anything to do with capture speed?
I still want to be able to use this computer for general normal computer stuff, including keeping Windows 7
Any recommendations on the Ultimate video capturing pc? while possibly re-using some or most of the listed hardware