I think I made an interesting discovery.
For some reason I always assumed classic theme would free up some resources. On newer, higher end hardware (mainly, GPU) I don't believe this does much if anything, but with Madvr I'm sort of on the edge of things using medium to high settings. In the past Windows did popup that annoying dialog that it believed things were slow advising to disable Aero. I went ahead and choose Classic theme.
Today I've been switching back and forth between classic and Aero. First with Madvr configured as follows:
With classic theme this seemed to work well, with rendering times around 12ms and presentation around 23ms.
I enabled Aero, and I was getting massive framedrops, stutters. Backbuffer queue was empty.
Next I enabled FSW mode in Madvr and rendering times dropped well below 10ms, presentation ~0.3ms with Aero still enabled.
I switched back to classic mode, expecting to see another improvement, but rendering times jumped back up to 12ms, presentation remained below 1ms though.
So for some reason, having Aero enabled with FSW mode (and maybe FSE too but I can' test that right now) I'm getting a good performance increase.
Maybe using that tweak to get Aero on your Windows version and using FSW or FSE could help you sqeeze enough of a performance gain out of your system to use Madvr after all. I think its worth a shot.