I have the R33 Brembos on my R32 but I bought the car that way so can't comment on the stock ones but I found the Brembos very good for the size they are even on our heavy GTR's. I have used my car on the track with the Brembos and they held up pretty good but would recommend a decent pad to go with them.
I have a r32 and went to the brembos with braided lines/discs/pads and also got the larger master cylinder bm 56 (get from a z32 as generally cheaper than r33 gtr ones if going 2nd hand)
I cant say it was night and day better but definitely an improvement-someone told me they are about 10 to 15% better and that seems about right. Worth doing if your brakes are knackered anyway