Now i ride with stock GSR cams. My setup is:
b16 pistons
0.25 milled GSR head
70mm TB
2.5 exhaust and header
What can I expect with s2s1 cams, what power gains, 1/4 mile and trap speed difference ? And what cam gears setting are good for me with 0.25 milled. What are the max effective rpm-s with s2s1 cams

 

Do you know what your Compression Ratio is at this point? Pro1 or Stage II tuner cams will do just fine with this setup if you have 11:1 CR.

 

I would stay away from tuners in general and go with a pro series cam for the best all around performance gains available.
To answer your question there are too many variable to get you an honest, true and straight forward answer. Every motor responds differently to each mod. With that being said THE BEST way to find out is install, dyno and race. Then you will have cold hard numbers for all your questions.
No cam gear is "better" than another so to say, they are basically just used for measuring cam timing. Whatever you like and fits your budget will serve you well. With that said dont get on ebay and type in "Cheap B-series cam gears"

 

maybe he doesnt have the upgraded valvetrain needed for the stage 2s or pro series cams.

to the op: props for not using type r cams

 

Props for not using type r cams? I just wonder why your saying that.

Regardless of upgraded valvetrain or not when running an aftermarket cams upgrading valvetrain is a must. period. Its even risky to run ITR cams on B16 or GSR valvetrain, it wasnt made for the added RPM or cam size. Yes its not much but whats the straw that breaks the camel's back in this case?