Steph...

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With my old Tower Computer; Windows XP Pro, 32-bit, Pentium 4 Dual Core Processor, 2.8 GHz, 16 GB System RAM, n-Vidia 9500GT, 1 GB Video RAM Graphics card; FS 2004 ran a treat, averaging a smooth18-20 FPS Frame Rate, LOCKED at 20FPS!
So...I suspect that you are over-stretching your Computer unnecessarily, Steph!
What I did with mine was to limit some of my various graphics settings to give me
SMOOTH scenery, which was my main aim!
Any thing that was not really necessary, I put a limit on in the settings.
Bit by bit, try by try, I achieved settings which gave me what I was looking for...SMOOTH Scenery....

...!
Very busy Airfields were always going to give me very low frame Rates (5-8 FPS) so I made a point of not spending too much time there....and their Coffee was awful anyway!
Open countryside was just fine, amongst the Cows and Sheep!
It all came down to carefully fine tuning my settings until I was happy...and I like being happy!...

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The same computer obviously gave me slight Frame Rate problems using FSX, and it was not until my old Pentium 4 Computer finally blew up, forcing me to get a fast £600 tower computer to run my FSX flat out.
But I did find that with careful adjustments, my old Pentium 4 computer was quite happy running my FS 2004.
..in fact I was so happy with my FS 2004 that it took me ages to change over to FSX!
Now, I have FS 2002, FS 2004, FSX, and CFS 2 all on my HDD ready to run at a moments notice!
The only thing I need now, is a 1942 Harley Knuckle-head, to complete my ultimate satisfaction....

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Steady-on Steph...

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Paul....MD....

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Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.