i am rooted, and i believe you would need to root to go back to 2.3.4.
when i was not rooted, i was at the newest version.
however, when i rooted, the root took me backwards to the "android version 2.3.4" and "kernal version 2.6.35.7", which i did not know it would do. i thought rooting it would leave it rooted with the MOST RECENT update intact. i suppose the root program i used did not root with the latest update and did not know enough to realize this.
from what i have read on the rooting section in android forums, most people prefer "android version 2.3.4".
in summary, to go backwards, i believe it depends on what rooting program you use to the version it uses/reloads on your phone.
i am NOT a rooting expert, and strongly recommend you also post in the rooting section as i do not want to give you bad advice. i had to have a friend help me, and i only wanted to share my experience.
good luck!!