If it works on 5.1.1 on one device, it's going to work on 5.1.1 for all devices. Either way, there is now a method to downgrade any device providing you have your SHSH blobs saved, so update if you want. But if you're on a 4S and you're jailbroken on 5.0.1 you'll want to wait until the jailbreak is released before updating.