Oh please !!
GS2 screen better than Xperia S ? Yes, in your dreams .
Xperia S has better screen than even the GS3 and One X when viewed head on. And the difference is quite staggering when you compare all the 3 side by side. If you can't do that then just watch such comparison videos on Youtube and read what the people who made those comparisons have to say about the Xperia S screen.
I have, on numerous occasions compared my Xperia S screen with GS3 and One X and let me tell you in real life the difference is even more pronounced than what you can make out in the videos below. Though as far as black levels go, no doubt the GS2 beats the Xperia S and also viewing angles. But then not everything you see will be a black screen and how many hours are you gonna look at the screen from an extreme angle ? I do wish my phone had black levels like the GS2 but whenever I watch a 1080p video on it, I forget about the black levels and just fall in love with the screen. On those rare occasions when you see a lot of black and you are in a dark room its fun to see the Galaxy S2 screen go pitch black but 95% of the time it doesn't even come close to giving you the WOW factor Xperia S delivers on most content. It's dull, almost lifeless in comparison to the XS when it comes to anything other than blacks.
And check Igyaan Xperia S video review. He has mentioned it has the best screen of any phone on the market today and that includes the Htc One X. Also check out GS3 hands on, he compared the GS3 screen with Xperia S and noted how much more vibrant and sharp the XS screen is.
And also who said performance is much better on GSII ???? Have you used an XS personally? If not then please refrain from posting such comments. A lot of people have upgraded from the GS2 to Xperia S and they do not feel so. Some feel XS is better, and some feel GS2 is lil faster.
Also check out benchmark scores, Xperia S beats GS2 in many benchmarks.
It's no fluke that the Xperia S is the No.3 best selling phone Globally today after the Iphone 4/4S and Galaxy S3. And trust me, most of the sales are due to the screen alone.