Do your edit in an adobe preset. You do not need the broadcast monitor for your edit. When finished and for color correction, checking legality (you need the scopes too) or for scene discussion and inspection you can always copy everything in a blackmagic sequence.
It could be a little difficult for BM to bypass the fact that Mercury acceleration happens in the graphics card. So if outputting from the BM Card I guess something's gotta give. On the other hand it is not clear to me if Mercury acceleration happens as process giving back an accelerated timeline for "everyone" in the system to use, or if it is something meant only for the graphic's card output. Maybe the BM team can shed some light as to how the API works, or if there is an API to tap into anyway.
Acceleration is definately there, you just get less layers than non-blackmagic project.
I get 2-3 layers or so. Depending on your needs it may be not enough, but it satisfies my needs completely as I rarely have more than 2 layers on the same time.
Im using Decklink Extreme 2, i7 920, gtx285.
I can understand completely why there is the lowering of performance in this case.
I've been following the matter closely as I'm about to buy the cS5 suite with HD Extreme III and don't want a duff setup.
However, it seems that the Aja customers are sufferinng bigger performance losses compared to BM, if you check their forum here.
I hope that as CUDA and GPGPU stuff advances that there can be more data exchange back to the other internal components like BM cards in the future.
Otherwise the solution is probably a Quadro card with SDI output (highly expensive) / some way of taking DVI or Displayport feed from Quadro card and linking from that to broadcast monitor through a converter... but lose a desktop screen in the process (unless you have SLI for extra monitor connections...)