I agree with Roy. The standard R33 brakes are the same size as R32GTRs so they cant be called small by any stretch.
The most logical question is WHY you want to upgrade? If you have found the brakes you have to be lacking then in what way?
If it is an issue of fading, most likely due to overheating then good pads, top quality fluid and potentially some decent discs should overcome any problems except perhaps the most extreme circuit use.
If it is a feel problem i.e. under hard braking the pedal seems spongy then a master cylinder brace would be the first step, followed by at least new brake hoses or possibly a step up to braided lines.
To get an idea of why, start your car, have someone sit in it and press as hard as they are able to on the brake pedal and watch the master cylinder flexing on the firewall. Often 5mm plus of flex is common and a brace eliminates that.
To answer Eds question. Stainless braided lines will not expand under high pressure like regular rubber brake hoses will. Rubber lines can look or feel great but even new ones will expand with pressure inside them, thereby reducing braking effectiveness.
My rant finished