My GTX 280 looks like it's good enough when I monitor ram & % GPU use

I'm just trying to understand where I could hope to get better performance WHEN I've upgraded to my next platform, which will be either IB or Haswell. The graph set attached is from a test flight out of ORBX's new KJAC. Of note, the big jump in GPU use happened concurrently w/ a hard stutter that happens on occasion, especially near complex airports, though not sure if this is a red herring or not. The hard stutter issue is something I don't believe I ever had until I installed FSDT software, though honestly I'm not sure if there is really a connection there or not. It's also quite variable, i.e., happens sometimes quite frequently, primarily very early in the flight, taxiing, etc, yet other times hardly at all. I've used procmon.exe and never saw anything solid there to explain this. I'm running a very lean Vista, not even Defender, no UAC, many other services off using GameBooster, no other A/V software, etc. I have generally wonderful smooth perf, just the hard hiccough issue. It is interesting to see the big GPU useage bump up as I say concommitant w/ the hard stutter event.

Tell me if you will if I kept the same single display & native resolution (1920x1200), 16x AF, 8xS or better AA, does it appear ...

• Additional video ram wouldn't be of value since I only got to 638mb max video ram use of 1GB available (averaged around 500mb)?
  
• A faster video card wouldn't really add much since the highest GPU usage displayed in the graph was only 70%, i.e., it never even used all that this card could do or so one could argue?
  

Thanks in advance for your insights & expertise,

Noel