I just purchased this aircraft yesterday and I am having the same problems. I have gone through the KB article that was suggested and selected the flight deck only option. I have also tried turning off the weather radar(added 3-5 fps) but I am getting really low frames even at high altitudes. This isn't a sound card issue, I am using a dedicated sound car and all my other payware aircraft perform fine.

Intel Core i7 920@3.2ghz|ASUS P6T Deluxe mobo|6GB G.Skill DDR3 1600|MSI 260 GTXOC 896|SoundBlaster X-FI Xtreme Gamer|500GB WD "Black" HD|Rosewill 850w PSU|Track IR4|Viewsonic 26 Inc LCD & Dell 2105 FP| Windows Vista 64 Ultimate