Sree,
Since you already know about the MTBF, a two stage synchronizer itself has a pretty good MT. Generally the rule of thumb is that the metastability resolves itself in a time period around ~20Th/su. So as long as your frequency isn't the limiter (ie. freq of operation is 20Th/su) a two stage synchronizer should do. In practically applications (systems designed at Ghz) we use a 3 stage synchronizer.
Much of what we contemplate here is just an educated guess any engineer makes at the expense of solid understanding of reliability.
-B