I know it's not related to your D2D question but there's some hilarious GDI benchmarks here:
http://www.tomshardware.com/reviews/2d-windows-gdi,2547-9.html (gdi polygon bench)
There's a link to the benchmark app somewhere and lots of results posted in the comments.
The summary of it is (given AMD's response) that since no one (in Toms or Anandtech and maybe few other sites) has bothered to benchmark 2D perf in past 10+ years, the companies haven't improved it, infact they've gone backwards, 2D is slower than 10+ years ago.
The benchmark figures aren't even the whole truth : Tom's have prettied them up by not including hw-accelerated GDI cards in XPDM results. So when you see Vista/7 being "only" 5 times slower than Win98/XP on some obsolete hardware from 10 years ago, it is really more like 10+ times slower since now everything 2D related is done in software and there's many more layers of abstraction now.
It may even get "better" in Windows 8. One of the build sessions suggested big perf drops in some old apps as DWM cannot be disabled anymore.