What is the fastest iOS version for the iPhone 3GS? I upgraded my wife's iPhone 3GS to iOS 5.0.1 and now basic tasks like opening apps like Texts/Phone dialer are now slower than before. I understand the 3GS is 2 years old, but just being able to type Text messages fluidly is a super basic task that a 600Mhz processor should handle just fine (as it did on iOS 4.x and 3.x). If not, Apple shouldn't be pushing and advertising iOS 5.x for 3GS's.

Anyway, what iOS version do you recommend I revert to? 

Although the iPhone is no longer jailbroken, I recall backing up the "SHSH blobs" to Cydia when it was jailbroken. So I should be able to revert to builds no longer signed by Apple.
Ok, so after some quick googling and reading some Apple forums, it looks like iCloud (in iOS 5.x) isn't ready for prime time. I've done the following and now iOS 5.x seems a lot snappier. 


Disabled iCloud everywhere (Settings -> iCloud)

Disable all apps then Scroll down and hit "Storage and Backup" and disable iCloud backups. If you really want to go strong, just delete your iCloud account setting (on your phone, Settings -> iCloud -> scroll to bottom)
Disabled sending data to Apple (Settings -> General -> About -> Diagnostic &amp; Usage -> "Don't send")
Minimized Location Services (Settings -> Location services)

I kept it ON globally, but disabled it for certain Apps
Most importantly, disabled it for "Diagnostic &amp; Usage" as well as "Location based iAds" (Settings -> Location services -> Scroll to bottom -> System Services)
Disabled notifications for the calendar (Settings -> Notification)

I also removed notifications for many other apps that had added themselves ...
However, I suspect this is fixed in iOS 5.0.1 under their "Battery issue fixed" patch. Earlier, Calendar notifications would hang causing CPU to be stuck 100%, draining the battery and leaving little CPU for other items.


Also, there are two apps, SysStatsMon and System Status. Both are good tools to see CPU usage on your iOS device. About 5+ seconds after launching them under normal circumstances, your CPU should be in the 5-15% range.