Engine revs vs mileage?

Here's a curious one...

Over the years, I've found my car seems happiest driving around 1800-2100rpm, and I gear accordingly.

However, I've been paying close attention to the MPG counter on my MFD, and it seems to return a much better mileage around 2500-2800rpm. I'm talking the difference between 35mpg at 1800 and 55-75mpg when up around 2800,

At the higher revs, the engine seemes to be really quite loud and it's just a bit beyond the point where the turbo starts tailing off. I'm not sure I'm happy driving with the engine this loud.

Does this seem right, or is it just a wildly inaccurate MFD?