My pair of Swarovski 10x50 EL's give me excellent performance. They have a great field of view and are crystal clear, mind you, they should be for the price. I can easily pick out colour schemes of the high flying overflights.
To be quite honest, anything over this is overkill. Even with a pair of 16x50's, unless they are a good quality make, what's the point. You are not going to read the reg at 35000ft, even if it's under the wings!