I have a doubt,whats the main difference about pixel shader 2.0 and ps 3.0?
Compatibility,speed i dont know

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it's speed, definatly, I see a big boost between 2 and 3, and 4

It should be speed but I dont think they make much of a difference really, newer GSdx revisions should select automatically the highest compatible in your card anyway so no need to worry about it much

Well thanks for your answers but i have a new doubt now,is there any difference (in speed i mean),betwen sm3 and sm4

In the case of GSdx Pixel Shader 4 can only be used in the Direct3D10 Renderer and in this mode you cant use Pixel Shader 3 so the real question would be DX10 vs DX9, in this case yeah DX10 not only increases speed but also fixes some glitches that appear in DX9. But as for general SM3 vs SM4 I am not really sure but I'd guess so.

speed is pretty much the only advantage with pixel shader 2 and 3. Some cards may not handle PS 3 well but be fine with PS 2, so dropping it down can sometimes have speed boosts.

This was a similar case to Nvidia FX5200 users on the old GSDX9, where there was a huge speed boost from using PS 1.3 instead of the slow PS 2

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yeah, less bugs on GSDX10. However, game runs may or may not faster than GSDX9 depending on what games you played.

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