Despite i have retired my Nexus S, yesterday power up to upgrade to Jelly Bean ( official).
Surprisingly the phone is not terribly slow once on Jelly bean comparing to Galaxy Nexus.. Jelly bean really smooth thing out.
Observation-Just after Jelly bean installation completed and back to the main screen, the initial minute was very sluggish,not so responsive to touch. after that...the phone became smooth and functioning properly however the auto screen rotation is malfunction.
After one more rebooot, the screen's auto-rotate back to normal and phone navigation is butterly smooth ,same level of smoothness like Galaxy Nexus..