Just had a thought, and decided to write it here before I forget. I very frequently go to anandtech for their GPU bench, or techpowerup for their gpu performance summary (techpowerup's summary has A LOT more GPU in the summary then most review sites).
Not that I want you to try to emulate what either of those sites have done, but some form of master GPU comparison tool that spans across reviewed GPUs is great. The ability to see how a 2-4 generation old GPU performs compared to a current gen is very useful…as those people will be very likely to be the ones upgrading. I know I have answered many forum questions using links to that type of chart or comparison.
I understand that it can be difficult to maintain a solid data set with limited variables over that time, so maybe consider a very small set of games along with power consumtion to use for a longer duration. IMO maybe 3 games covering a range of developers and drop GPU out of the chart once 4 gen old. Or you could phase them out...for example have all gtx 9/7, but then maybe only 680/660, 580/560, and lastly a 480.
Obviosuly that is just an example, but I believe it would be a good idea to develop as the site progresses.