The Landscape LOD texture replacement that fixes those blurry distant ground textures, just fixes the blurry distant land textures that come with the game.
And does not effect performance AT ALL.
Once you have the game installed, you'll see.
As for the other tweaks on the site i linked to, different people report different results. (of course)
Ive tweaked the game for a X1900xtx, x1900xt, 7800gt, x1600 for myself and friends and everyone was very pleased with the results.
(better image quality and better performance)
So i personally feel the tweaks on that site are worth it.
As well as several other tweaks ive done to get the game running smoother outdooors on a 7800gt and a x1600.
Just wait until you have it installed and dont do any "tweaks" or mods ....play the game until you are outdoors and see if the default settings that came with the game are acceptable to you.
If not, you'd be amazed what can be done with a little effort and tweaking.