Mike,
Seems it's the old post processing problem again. Looks okay with it off but getting this when it's switched on:
I know that on my machine (twin GTX 480s in SLI mode), I had to turn Pinball Arcade's AA off and then set up a profile for TPA in the nVidia configuration and tell it to override 8x AA on. For some reason my cards don't like TPA telling them what to do.Looks like AA is disabled. There is an issue I haven't been able to track down where on some GPU's you can't have post processing and AA on at the same time. The odd thing is it's not specific to manufacturer. I have a nVidia GTX 660 in my work PC and it works here. I'll pass it along to our engine guy and see if he has any thoughts.
One thing you can try is using nVidia control panel and override Pinball Arcade to use AA in there.
If you look at Log.txt in the same location as the PinballArcade.exe what does it says for Set Display Mode?
Output would be something similar to
Set display mode
Resolution = 1920x1200
PixelFormat = 22
DepthFormat = 75
StencilBits = 8
Does it work if you force AA and AF settings in the nvidia control panel? I have TPA set up that way and it looks good at 1440x2560. Better than whatever the game looks like using its own settings.