I was sure Barry mentioned this here before but I don't see a thread specifically for OrbX so I'll start one.
I bought only one so far, but am budgetting for more for sure. I got the Northern Rockies. I posted some shots from the multi in that area last night and reported that my frame rates fell through the floor around Calgary. I didn't mind because I'm used to that in cities - I try to keep all my sliders maxed out and as long as FSX keeps chugging along, I'm much happier than I was with 100 fps and low autogen in FS9.
But today I had a look at the FTX manual and tried their FSX settings, since their scenery provides the autogen now. I'm happy to say that on a short test flight in YYC, I suddenly got very good frame rates - ~45 fps. This will take some tweaking, but it looks like those guys at FTX have done a great job on the programming as well as the look.