I cant speak for Bangalore, but for Mumbai, my colleague has told me that the speeds are great.
However, the coverage is not exactly great, so till they do a complete rollout, I would suggest to wait to port out.
Oh, and Vodafone too are planning to come up with 4G rollout later this year or early next year. Cannot confirm, should be taken with a pinch of salt, since it is a marketing honcho's words