Dear God, (never thought I'd email you,but...)
I've been wanting to post this hint I just found last week. This may help you and others. Setting auto and boat traffic to ZERO improved my frame rates by 5-8 fps. This won't solve your problem, but might help, plus it gets the hint out to everyone it might benefit.
My system is inferior to yours (Pentium E5300 2.6 GHz, 4GB ram, GeF 560). My f/s is currently set for 24. I now get 14-18 f/s in VC, 24 in other views.
I read this weekend that PC (therefore, FS) gaming sales are small change to software companies, (compared to Playstation, etc.), these days, and that serious FS programs are unlikely in the future (we are a relatively small community). I will likely upgrade to a i7 3.4+ GHz, 8-12 GB RAM, GeF 620 system and live with FSX and PMDG for the next few years.
Check jetlinesystems website for some great FSX computer updating ideas.