Would you classify a GTX 285 that runs as a GTX 280, rare?
What is this sorcery, you say? Well, I'll tell you (here's a TL;DR version).
GTX 280 had fan issues from my SLI setup. Sent RMA to BFG - they sent back GTX 285. I now had 1 GTX 280 and 1 GTX 285. GTX 285 was unstable, constant driver crashes. I adjusted voltage up/down and clocks up/down - no change. BGF had closed doors right after I got my RAM filled and I couldn't send the 285 back in. 285 wasn't stable, no matter what I tried. Last ditch effort, flash my working 280 BIOS on the 285 and it worked. I ran the card for another year and then my younger brother used it for the past 4 years.
(GPU-Z validation link:
http://www.techpowerup.com/gpuz/details.php?id=n8bde)
Here's a pic of a GPU-Z shot of an actual GTX 280 - notice the die size difference:
The card was in disarray when I got it back from my younger brother. It was clogged with dust and the front graphic label was peeling off. I had to re-adhere the label on as best as I could. I had to spend some time cleaning her up - while she's not in perfect condition, the new TIM and removal of dust bunnies lodged in her heatsink have her running cool again. I couldn't bring myself to take before pics, but here's the after pics and installing her to test in my PC.
I ran her under 3DMark Vantage, my results are here:
http://www.3dmark.com/3dmv/5389525
Here's a GTX 280 result I found to compare against mine:
http://www.3dmark.com/3dmv/429736
She topped out at about 72C during the benchmarking -which is around the norm from when I remember using the cards.
The graphic scores are very close. In the Graphic Card information for my run, you'll notice it calls my card a "Generic VGA". A bit further down it recognizes the Driver Name as GTX 280. She still works great and as much fun as it was to run the old beast, I'm going back to my GTX 980Ti. I hope you enjoyed!