Sony has stated that they will roll out ICS update for Sony Xperia model in Q2 2012 and hey, it's mid April and right now, they have already roll it to public. According to a post in XPeria Blog, there hasn't been any increment/decrement after upgrading to the latest ICS. FYI, the information used by XPeria Blog was Sony XPeria Arc S which has 1.5 GHz processors.
The new update is using Linux Kernel 2.6.32 which is a long-term kernel releases. The ICS version that is rolled out is ICS 4.0.3, not the latest version that was released by Google (4.0.4)
Among the changes are quick dial, new recent apps viewer, quick response
for incoming calls, improved email app and better monitoring &
control over mobile data. To maintain an optimal user experience, they
have included a Performance Assistant which lets you disable certain
apps from running for better performance.
Let's see if my wife is willing to upgrade her phone to ICS