Sylvia is going to rue the day he pressed for this quick re-match. I believe that Arlovski will take the title back sometime in round one via submission. Andre is a very smart fighter that learns from his mistakes and I doubt he will allow Tim another chance to take this fight from him.
If I was Sylvia I'd be sleeping with that belt every night and enjoying the limited time I have with it.
As far as Ortiz and Shamrock... I'd have to say that Ortiz is most likely to win this fight. Ken is no pushover by any stretch and he isn't coming off a knee and back injury like Tito is so he certainly has a punchers chance of winning the fight.