Actually it's not totally for James but I noticed that James posted quite a significant defense for FSX vs FS9. I tried to switch 8 months ago but realized by specs ould not handle it. I would like to reconsider and I was wondering what, if any, existing hardware specs would run FSX (with all the add-ons) at at least 20 fps in the most intense locations (over JFK for instance).
James..I'm really interested in knowing if you achieve those FPS with all those nice add-ons you have for FSX (FEX, GEX, FSDT airports, etc). What are your specs and what is top of the line right now? I think you also mentioned there would be some new hardware out this fall. Wondering if it's worth the wait?
Of course the question above applies to anyone who can help, I'm just picking on James because of his "sell me FSX" post not too long ago! Hey..it got me interested! 
jcupido,
To get back on your subject, I built a new system last April '08 just for FSX for about $1800. The price of course doesn't include a monitor, keyboard and mouse because I am using the same ones from my last system.
Anyway, the system I built constits of this:
* WinXP Home SP3
* INTEL Core™ 2 Duo E8400 3.0GHz oc'd @ 3.85 GHz
* ASUS Maximus Formula Intel X38
* CORSAIR, 2GB (2 x 1GB) XMS2 PC2-8500 DDR2 oc'd @ 1080 MHz
* XigmaTek HDT-S1283
* EVGA GeForce™ 8800 GTS 512MB
* WESTERN DIGITAL 500GB * WESTERN DIGITAL 250GB
* ANTECH Nine Hundred Case
* PC Power & Cooling S75QB 750W 80 PLUS Certified Active PFC Power Supply
After the build was done I used the FS-GS service to do the OS, drivers and FSX setup. You could also use NickN's guide for free.
Anyway, I am using all the main addons like UT2, UTX, GEX, ASA, plus other addon aircraft, airports, and photosceneries. All in all I get great performance with most setting at or near max. The only setting I don't use on a consistant basis are bloom and lens flare. Flying into major hubs in the LDS767 with 80% to 100% AI and with cloudy weather I usually don't drop below 18 fps but maintain about 25 fps and in other less dense areas I can get anywhere from 30 FPS to over 100 FPS.
The one thing that I do however is use unlimited frames in dense areas and locked frames at 28 when in less dense areas. When I start to get the FPS bouncing from 30 to 90 FPS it starts to get a little choppy. Locking the frames in these situations removes the stutters and makes it smooth.
I think that you can build a great system for less than $2500 and get really good performance. I think that to get the most from FSX you will need to get a CPU that has at least 3.0 ghz per core and a video card that is no less than 512 mb. My CPU was 3.0 ghz stock and I overclocked it to 3.85 ghz. I get slightly better performance than I did at 3.0, but it leaves me a little more overhead when I am in dense areas with heavy weather and lot of AI in the area.
If I were you I would stay away from factory built systems like Dell, HP, etc. By either building one or having one built you can buy much better components and taylor the system to your needs for usually cheaper than buying a prebuilt. In my case I bought all the components and had the system built at a shop for about $100 and it only took them about 4 hours to do.
I wouldn't be discourged by a lot of posts you may read about performance in FSX being horrible. Even with my slightly older system I can run FSX pretty much all out and get great results. In fact, it looks and performs so well that I don't even use FS9 anymore.
Just make sure to buy good parts, have the operating system, drivers, FSX set up correctly, or pay someone like FS-GS to do it for you and you will be happy for no more than a couple thousand bucks.
Good luck.
