Best way to create a ground

Hello everybody, i'm Damien , flash coder from France.

My question is the following : what is the best way and what are the tips to create a ground with a large textured plane for a a pv3d game.

I m searching for long now but i can't find a really good compromise.

If i use a detailed plane (30x30 segments ) the rendering is correct  but the number of triangles is pretty high and FPS drops down.  

If i use a less detailed plane ( 20x20 segments ), the number of triangles really drops down and FPS is good, but the straights lines on my texture don't look straight anymore.

What are the tips to optimize a large plane preserving most of the quality ?

Thx !