Smarter to buy Galaxy Nexus than Galaxy S3 because of Jelly Bean upgradability?

Despite being older and having worse specs than the Samsung Galaxy S3, would it make more sense to buy the Galaxy Nexus because it will likely be the first phone to get Jelly Bean?

Jelly Bean is supposed to make movements/screen response more smooth (Project Butter) and make OS appear faster.

Since the Nexus would get this update before the S3, would the performance improvements from Jelly Bean outweigh the better specs of the S3?

Also, how quick is Sprint to release updates for the Nexus? Would it take just as long for Jelly Bean to be released on the Nexus as it would the S3?

And while I know that everything surrounding Jelly Bean is, at this time, purely hypothetical, I'm mostly asking about previous release cycles/trends