About SDRAM clock ! ?

That should have worked (assuming you use the clock crossing adapters in SOPC Builder). The million dollar question is what did you delay the clock with (if you speed up the clock you want to keep a constant time delay but in terms of degrees it should have doubled from what it was at 50MHz). So the phase for the SDRAM clock at 50MHz was probably -72 ish, and so this becomes -144 degrees at 100MHz (I'm assuming a Nios development board here).

With that said, I don't recommend running a Nios processor at a different clock speed as memory (being able to run the CPU and memory at the same speed is one of the advantages an embedded processor has over your PC sitting on your desk). Depending on what's in your system I could probably recommend a mix that will give you the highest performance possible (i.e. need more info).

Cheers