mick1, I have just gone through the process of getting a new system with FSX in mind.
I tried several systems over the last 3 months or so and settled on the following which I bought a few weeks ago.
500 watt Cooltech PSU
E6850 3 gig Core 2 Duo CPU
DP35DPM 'Dragontail Peak' motherboard
4 gig 800 mhz Kingmax memory
160 gig FAT32 hard drive
500 gig NTFS hard drive
V8803GT52R2 Graphics card
Things I found in the process and things I would change if I did it all over again.
Initially I tried the 8800GTS640 and was very dissapointed in it as far as FSX was concerned.
I then actually settled on a 8800GT512 which was pretty cool (cheaper also) but the AA did not work.
Fortunately for me it packed up and all the company could get me was this V8803GT which I had never heard of but said ok, what the hell it is a 8800GT512 at the end of the day.
That was a good move as this is the revision 2 OC version of the 8800GT512 with the Anti-Aliasing fixed, DDR3 etc, and it rocks.
It alone requires 120 watts odd hence the extra strength power supply.
I also initially started off with a 500 gig C drive but found FSX took for ever to load so being a DOS Assembler freak, I switched to a smallest drive I could find, in this case a 160gig and formatted it with a Win98's DOS 7.1 FAT32
Installed WinXp Pro and SP3 and my startup time is now twice as fast.
I then installed the 500 gig drive as my D drive.
Overall I am extremely happy with the system and it did not break my bank.
The only thing I would change is the motherboard and rather get the D975XBX2KR 'BadAxe2' board.
I really battled to get the 8 channel sound working correctly on my motherboard as apparently it is known that this board gives sound problems.
Anyway after much searching on the net I found a solution but will probably still get a soundcard just to be safe.
See picture of Seatle in FSX at 1500 feet with 38 FPS ave - goes between 32 and 46 - everything on High and Scenery on Very Dense etc.
On my older PC (2.6 gig - 6600GTS256 - 2 gig mem) I never saw better than 8-14 FPS anywhere.
http://www.proasm.com/images/pics/seatfsx.jpgBtw, in FS2004 with same pic I get 60 FPS ave.
I too have the Logitech Extreme 3D Pro Joystick and it is great.