It depends upon if you're using a one-way, solid or diff. The split between front and rear plays a big role in the performance of the car at the entry and exit of the corner.

I find for certain that when I run a 3mm split, the turn in isn't quite as good as when I run 2.5 or 2mm split. But less split than this starts to affect to steering at the exit of the corner (i.e. less)

Regarding braking, it doesn't really affect the braking performance at all, but may allow you to carry more speed into the corner depending upon this split you use.

Julius wrote a great article about the 21T, which explains the different possibilities: click here.

Cheers, Mark.