If a shoe doesn't fit in your measured size, then it's the wrong shoe. Sizing-up just causes more places for the shoe to fit wrong. A square peg will eventually fit in a round hole if you make the hole big enough, but it won't fit properly. The flex point can be less of an issue in stiff soled bike shoes, but the rest of it should fit in shape, volume, and width, regardless. I've tried a bunch and the sizing is clearly meaningless or the shapes and volume are completely different. You can't go by brand either, but by individual model. Each model will fit differently, typically.

It looks like 27cm should be a 43.5 European which is usually, but not always a size 10 US. That's about the same size I wear in properly fitted shoes, but not all are labeled 43.5 European. I don't think I've ever noticed a mondopoint(mm) on any labels.