It does not matter much if you are using DOT 4 or DOT 5.1.
What matters more is what type of DOT 4 it is.
The standard boiling temperature of DOT 4 is:
DOT 4 base
And a few of the racing ones are below.
As you can see its more about which brand / type you chose. I alway like the Castrol SRF, but its bloody expensive, at 45 pounds a bottle. Though it lasts a year or more on the track with no problem, (so pay once rather than two three times)