Ok, I've tried X.org backport for Debian stable. I've used this apt repository:

deb http://people.debian.org/~nobse/xorg-x11/ sarge main

Everything went well, but for some reason my (developed) video applications runs more slowly on certain hardware...
So now I want to go back to the old ( ) XFree86 4.3, wich has best performance for me.

But I've notice, after installing XFree86, the xlib libraries installed with X.org wasn't unintstalled has expected (I know... 6.8 is a greater version than 4.3 ).

My question is: is it safe to execute a dowgrade for all those libraries? I can use X.org libraries on Xfree86 binary (at the moment everything goes pretty well, excluding my applications), but I'm little scary