Will I Benefit By Upgrading Video Card Only? or Complete New Build?

Question

I, too, was wondering if I might benefit from upgrading only the graphics card. My current system:
Windows 7 Ultimate 64-bit SP1
  CPU
   Intel Core i7 2600K @ 3.40GHz 43 °C
   Sandy Bridge 32nm Technology
RAM
   32.0GB Dual-Channel DDR3 @ 799MHz (10-10-10-27)
  Motherboard
   ASUSTeK COMPUTER INC. P8Z77-V PRO/THUNDERBOLT (LGA1155) 37 °C
  Graphics
  1535MB NVIDIA GeForce GTX 580 Amp! (ZOTAC International) 44 °C
  Storage
  CACHE & PREVIEWS 111GB ATA KINGSTON SH100S3 SCSI Disk Device (SSD) 34 °C
  OS DRIVE 238GB ATA Samsung SSD 840 SCSI Disk Device (SSD) 35 °C
  CAPTURE STORAGE 16 TB Intel Raid 0 Volume SCSI Disk Device (4 x 4TB) 34 °C
     DNxHD 220 Footage
     DSLR Footage
     AVCHD
   Optical Blu-ray Drives
   HL-DT-ST BD-RE BH16NS40 ATA Device
I was shooting HDV when I built this system, but am now shooting with a Canon EOS C100 and a 5D Mk III DSLR. I record DNxHD externally onto Atomos Ninja Blade.
Although this system seems pretty well balanced, I have never been able to do much more than basic editing with Premiere's real-time effects, since anything else (like Noise reducers, MB Looks and Red Giant effects) pretty much cripples my system playback, rendering, exporting. Even with HDV footage I was never satisfied with performance. I recently upgraded my storage from a 2-disk RAID 0 to a 4-disk 16 TB RAID 0, which seems to have helped transfer rates a little.
I wonder if the GTX 580 is defective.  It seems to run pretty hot under load at 60 degrees or more unless I boost fan speed to the max. I cannot change any GPU clocks speeds or other settings from default without the display crashing. That is why I am considering a new GPU. I plan to build or buy a new PC within the next year, anyway, but it would be great if a GPU could extend the life of this one.
As for a new complete built, I need to know if now is the time to do it. Or, is there some new motherboard/processor series on the horizon that I should wait for? The frustrating thing about these kinds of forum threads is that the information is quickly dated and obsolete.

Answer 1

I am hardware accelerated.
As for the GPU temperature. The NVidia control panel monitors voltages and temperatures, but gives no reference for what the normal operating temperature should be. How do I know if the GPU is running too hot? The same goes for the rest of the components. I'm sure you professional computer builders have that kind of info available, but how do the rest of us know when something is wrong with a component? Is there a troubleshooter I can download? or a chart that shows a normal range of numbers?
When I first built this computer 3 years ago or so, I had a GTX 470, but it fried a year later and I replaced it with the GTX 580, which gave me a good boost in performance over the 470. It would seem that a 700 series GPU would give me better performance over the 580 - with a vast in increase in CUDA cores and more RAM, etc. But, I have read in this forum and other places that a newer model GPU alone will not make much difference, which makes absolutely no sense. If that's true, then what's the point of having all those additional CUDA cores?