First off, you should have posted this in the FSX section...But I can help you here anyway.

GEX, UTX and REX all do different things to FSX that both improve the sim and complement each other.

GEX replaces the ground textures (how the ground looks from the air) with ones that look more like the actual ground in a given area in a given season.

UTX replaces and enhances what, where and how much stuff is on the ground.  Example:  My grandfather worked for a railroad.  His home station was the Memphis, TN yard.  Default FSX has no rail yard where he worked.  The tracks go thru there, but no yard.  UTX puts a rail yard in the appropriate location and oriented in the correct direction.  Other enchancements put cemeteries, parks, racetracks and other features.  They may not match the real stadium or track but it is there in the approximate place the real world building or feature is.  There is some slippage but the overall is quite accurate.

REX is a weather and flight planner addon.  It can be used to fly some darn realistic flights.  I "fly" out of Millington, TN Municipal Jetport.  I have driven to WalMart in the grey rainy then come home, set REX up for realworld weather and took off in a freakishly similar environment I was just in out in the real world.

I would get them all.  They require some trial and error to get the best mix of features, but the experience is worth it.

GEX US/Canada, UTX and REX 2.0.  UTX is offered only for the US, Canada, or Europe as far as I know.  I have them all.  GEX is offered for the US/Canada in one package and for Europe.  REX is one size fits all.  I would get the DVD versions if I were you.  Flight1 Software is the go get place.  They offer download and DVD for all.

Request this be moved to the FSX forum and I will try to help you get FSX smooth and Wowed up.

The Evil Unkie Strikes!