If you apply full braking pressure on dry pavement (in ideal weather for your tires), can you engage ABS? If the answer is no, then Brembos will improve your braking ability. If the answer is yes and you don't road course your car, you need better tires to take advantage of a Brembo upgrade.
Despite what some people here are saying, the 4-piston Brembos will absolutely apply more braking force than stock. They do also hold up to heat much better, but that's a non issue for most people. I wouldn't go up to 6-piston unless you just want the looks of the huge rotor and caliper.