Brother i respect your experience but every one has their own opinion. I have also used iphone 4s and s2 a lot. And Own S3 and note 2. Iphone has closed operating system (object C), no customization at all. That is why it is most of the time lag free. But just install pure stock andriod on S2 and then see its power. Even i liked the display of s2 as compare to iphone 4s, even it has more ppi than s2.
Modern Combat 3 is not at all optimized game in android. Major advantage of IOS is that all games are optimized on IOS so Iphone will lead in games category every time. Except that, no comparison between IOS and ANDROID.
And i would recommend you to stick with your iphone 4s and wait for iphone 5s. It will definitely be an UPGRADE.