All the testings were done in DX10 mode.
I followed Word Not Allowed's guide to tune my FSX CFG except the bufferpool part. I use RejectThreshold=262144 and PoolSize=5000000
Turning down setting in DX10 Scenery Fixer didn't help much, My fps still struggles around 15. However, switching to DX9 seems to be a lot better. Although my FPS is only 20ish, it feels much smoother compared to what I get in DX10 mode. I suspect the scenery isn't optimized for DX10.
One more finding, the performance of Terminal 1 seems to be somewhat better than Terminal 2? I find that when I look at terminal 1 my FPS is a little bit higher that terminal 2 ie. 3-5 FPS boost. Don't know whether this is true or just my illusion.