How do you use your car, and what other upgrades have you made to the braking system?
For normal road use, there is absolutely no benefit using anything other than bog standard DOT4 from the nearest motor factor.
If you track it, if you've upgraded to braided hoses, if you've got upgraded pads/discs/calipers and you expect to reach the point of brake fade, then
you should think about using DOT5.1 instead.
The main difference is the boiling point of the 2 types - DOT5.1 has a higher boiling point, but for normal road use this is almost completely irrelevant