What, did you expect him to run 3DMark11 at native resolution before he popped out the old card, and after he popped in the new?
The extra GB of VRAM makes a world of difference at native resolution on the 27". But finding benchmarks for that resolution is hard.
Earlier I was looking at the benchmarks for the AMD 7970 vs. Nvida GTX 680 running at 4K. Upgrading from 2GB to 4GB VRAM improved performance by about 50%, much to the shock of the reviewer. While I don't have "hard numbers", I'd guess the performance gain on the 6970m at 2560x1440 going from 1GB to 2GB is pretty similar.
Nope .. but I believe that doctor replaced his iMac GPU from 1GB to 2GB, means he experienced both and claims to noticed improvement.
So instead just saying "I noticed a HUGE improvement" he could at least state, what kind of improvement. With what app? Doing what activity?
With 1 GB GPU he could do that in X seconds or FPS
With 2 GB GPU he could do that in Y seconds or FPS
So extra VRAM allow me to finish the job in (Y-X) seconds faster or more FPS.
Or give a rough estimation if he couldn't provide the exact difference, instead of saying "HUGE" or "SIGNIFICANT" ... it's all too subjective.
Claimed to have a Ph.D title, craving numerical proof should've came first into mind instead of meaningless crap like that. I provided a valid data and all he could say was "don't believe this bozo and his flipping chart." .. Why not provide another valid data or argument to prove me otherwise?
EDIT:
Look man ... with all due respect, I don't mean to be a troll here. For goodness I love this forum and I'm trying to contribute the best I can.
I do feel silly and tired for debating over this thing again and again. But as I told you earlier, I have an iMac with 2GB VRAM myself, so I'm not trying to justify my machine or being envy and all.
I played BF3 on it months ago, set most to ultra on 2560x1440 (no AA/AF), I got a merely thin 20fps (almost stuttering). Compared to reports from iMac with 1GB GPU owners, I noticed roughly the same result, some 1GB GPUs even get a bit higher average FPS than mine, I could safely assume it's a redundancy.
So I do think even with 2GB GPU, high resolution, ultra texture pack .. my 6970M has yielded to its limit way before it could fill up the RAM. In short, 2GB is too good for it.