I had a deeper look into the performance.

As always when renering to rtt antialiasing is a painful issue.

In my original framework I rendered into a rtt which was scaled twice the screensize

[code=cpp]  
<!-- default auxiliary buffers (auxIn, auxOut and rttDepth)-->
  
<RenderTarget id="auxIn" colorFormat="10" scale="2.0" />
  
<RenderTarget id="auxOut" colorFormat="10" scale="2.0" />
[/code]


downscaling2x2 in the finalpass leads to an acceptable antialiasing effect (at the cost of framerate).


Now I experimented with the fxaa algorithm designed by Timothy Lottes ([url]http://timothylottes.blogspot.com/2011/07/fxaa-311-released.html[/url]).
I included it into the framework and it gave me a significant boost in terms of framerate.


You can find the project here 
http://www.mediafire.com/?9g9cr1n75364zr5.

with the fixed glsl code by christianclavet (big thank you for this!!!)

http://oi54.tinypic.com/24zf048.jpg

Unfortunately I didn't get it to work wit openl.