Steph....

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Four of my favourite add-ons for my Flight Sims are "Ultimate Terrain USA", "OrbX FTX Global", "Accu Feel" and "Instant Scenery 3".
UT USA and FTX Global dramatically improve the realism of my FS 2004 and FSX with no noticeable frame rate hits, either on my previous Pentium 4, 2.8 GHz Processor, or my present Intel i7, 3.4 GHz Processor!
"UT USA" brings the whole USA scenery to life, with its roads, railways, waterways, and coast lines..
...and "FTX Global" shows very accurate scenery mesh!
("FS Global SE" for my FS 2004)
Whichever add-on you have, either for FS 2004 or FSX, they are always worth a try!
"UT USA" is particularly realistic on FSX because of FSX's moving traffic!
My daily USA scenery flights are highly realistic, according to Videos and Photographs I see!
If you like "scenery", you wont be disappointed with "UT USA", either for FS 2004 or FSX!....

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Paul...touring UTAH, Zion National Park, Bryce Canyon, in a Cessna 150....(and pretending I am on a Harley Davidson Street Glide!)....

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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.