With so many terahashes flying around, would a fast internet connection be of any help, or an average speed one will do just as well, since everyone has the block that is being worked on?
I looked up a recent block, it had 18 leading zeroes in the hash that solved it. 18. The chances of making a hash that fits that criteria are very low.
Your internet connection has nothing to do with your chance of finding a block, however, finding and actually winning a block are two different things, of you have high latency to other nodes (especially pools' nodes) it will increase your chance of orphan blocks, but to be on the safe side, you do not need a super fast Internet or anything like that, just a steady connection and better yet use a pool that knows how to propagate blocks in time.