Personally I wouldn't bother upgrading the rears, but if you are dead keen the 33/34 brembo rears have been working fine on my race car for years. Just use more or less aggressive pads if they lock up before the fronts
To really bother upgrading the rear you need to have either removed a lot of weight from the front, or shifted a lot of weight rearwards. Standard weight distribution is about 2/3 front and 1/3 rear when static, and it is even more due to weight shift when you hit the brakes. As a result the rears do 9/10ths of stuff all.