Advice on my component upgrade. From gaming rig to video editing rig utilizing Premiere Pro CS6.

Okay, Here is the dealeo. I built a rig that's a few years old now & isn't cutting it anymore. It was mainly used for work (I'm a plumbing contractor) & some basic video editing (was a noob to video editing). I used the 3 monitors mainly so I can view plans on one (or two) monitors, write contracts on another, email, etc.. Also quite helpful with graphic design & video editing.

I consider my level of PC hardware & software experience to be maybe a 5, on my 1-10 scale.
(a 1 being an 80yr old person that has never turned on a PC & a 10 being someone that has worked in the IT field for 20+ years). I've been toying with PC's since I was a kid in the mid 80's. My first machine was the Commodore 64. I've built maybe 20+ systems over the years for myself & for other people, usually family. I've never really worked in an IT field, per say. I do all of my own marketing & graphic design for my company. I have an AutoCAD degree & have taken some other related college classes like MS Office. People I know (usually older than me, 38+ yrs old) ask me when they don't know how to do IT stuff. I know enough to know, how much I really don't know.

I feel the need to upgrade because I'm now integrating on-site video in to my company website. I edit & encode with Adobe Premiere Pro CS6. I use 3 GoPro cameras on the "r3" setting 1280 X 720p @ 60fps. Usually only two at the same time. One chest mount & one head mount. The camera settings are r3 because I like being able to pull quality stills out of the footage & the cameras are rarely in a stationary position. I'm trying to use multi-cam editing (2 cameras) on Premiere & I get crappy playback. Almost impossible to use the multi-cam feature in Premiere Pro CS6. Also seems like a long azz time to encode something for YouTube uploads.

I'm not sure where the bottleneck is, and to what extent I need to upgrade my system to overcome my issues. I also have the 3D accessory for my GoPro cameras & I'd like to be able to produce some 3D stuff in the future.
BTW nothing is overclocked.

CURRENT RIG:
Display = 3 - 28" 1920 X 1200 @ 60Hz monitors (I-INC HSG1065)
Video Card = 1 - XFX Radeon HD 6870, 1gig RAM
Mainboard = MSI K9A2 CF V2
CPU = AMD Athlon 64 X2 dual core 5800+ 3ghz
RAM = 8gigs of OCZ Reaper
Storage = 1 -128gig OCZ Vertex 3 SSD for my Win 7 Pro 64bit OS, CS6 & other programs
1 - 1tb Seagate Barracuda HDD 7200rpm ST31000528AS (general long term storage)
1 - 3tb Seagate Barracuda HDD 7200rpm ST33000651AS (primary desktop storage device)
1 - 1.5tb GoFlex USB 3.0 drive ST1500LM003 (use as my short term video storage drive)
Cooling = 1 - H100 CPU cooler, 2 - 120mm Case Fans
Case = Generic Mid tower
PSU = FX PRO850W

PROPOSED RIG:
Reuse Displays, Storage Devices, CPU Cooler, Case w/ PSU:
Mainboard: Asus Sabertooth Z77
CPU: i7-3770K (Ivy Bridge, Quad Core, LGA 1155)
Video Card: MSI N670 GeForce GTX 670 (2gb, 256-bit, PCI-E 3.0)
Ram: Corsair Vengence 16gb ((2 X 8gig) DDR3 1866 Dual Channel Latency 9-10-9-27)

Please let me know, if you know of any capability issues with these components.
Is this overkill for smooth multi-cam playback with Premiere Pro CS6?
Can I just buy the GTX 670 card to get smooth playback on my current system?
Would different components in the same price range or less be just as good or better ?
Does the GTX 670 require anything special for a 4 monitor display, 1 one of which @ 120Hz ?

Thank you for your help.

Sincerely,

Michael.

My card (Radeon 6870) does NOT support mercury. It DOES max the CPU's out. My current build didn't factor in the possibility of any video editing or encoding. I am kind of a noob when it comes to comprehending how the GPU & CPU work together. Please correct me if I am wrong, because up until now I've never needed to process & export video at high speed.

During playback, My understanding is that the more CUDA cores one has, the more HD video streams one can playback at a given time (assuming other components are not bolltenecking). i.e. more playback bandwidth is available.

During encoding however, The CPU is the key/only factor to encode (export) video faster. Does the GPU &/or CUDA cores have any effect on encoding times ?

How would having two GTX 570 cards w/ 480 CUDA cores each on SLI, compare to one GTX 670 card w/ 1344 CUDA cores? Playback &/or Encoding? How would a "workstation" card or cards of similar price range ($300 - $400) effect productivity compared to a consumer "gaming" card? Does it come down to FLOPS ?

I'm looking at the Matrox Compress HD card & wondering how significant this device would be for reducing my encoding times with the new build. The h.264 seems to be the standard. I guess I can always add this card later.

I appreciate any/all feedback.