I have answered my own question, E46 BMW stock brakes are generally poor because only recently have BMW equipped callipers with more than ONE piston

as such, upgrading brakes for anything other than OM/OEM is pointless unless you spend another £1k getting an uprated brake kit (2k for all-round) which will get you pretty decent braking but what for? unless you decided to spend another 3-5k on upgrading the engine and other parts it seems a very pointless exercise