Like I mentioned I've got a Ge4400 Ti 128mb card, which is even older than his 5000-series card, and I get pretty good fps under almost all situations. Granted it doesn't look so great, I get problems with smoke and lots of problems with fire balls not showing up properly, but I suspect that's because it's a low end system.
The benchmark is to go offline, move to a CV, up and set the b24 on fire, then look out at the B24 and the CV in the same frame and see if you drop below 30fps. The idea is that the fire trail eats up fps big time, as does ground detail (simulated by the CV, which has a lot of detail to display, and also eats up fps).
If you can hack a burning B24 over a full CV battle group at low alt, you're golden.