AFAIK Microsoft's .NET runtime has also made significant improvements in the last 2.5 years, so as I said, it's just a thumb-suck as to whether the gap has changed. Maybe this will get someone interested in doing some comprehensive benchmarking...
In recent experiences, .NET runtime is faster in most situations, but sometimes Mono can be faster than .NET. It all depends on what you are doing. In extreme cases, .NET is usually ahead. You also have to account for the JIT time. It's after the JIT that should matter.
