I looked into this a while ago and yes the 5/6 brakes will go on to a 4 if the wheels allow it. If you want to take a chance with the Brembo's, it's probably the cheapest option especially if you can pick some up second hand.
I have been asking few times about the Brembos for Evo4...
Because it will be a cheaper option to go for...
I believe my 17' OZ Sinfonia is able to clear with those Brembos..
So Can I just get the calipers only? Or I need to have the whole brake kits include discs and pads...plus other extra?
What about the offset difference (ET46 offset on 4)??? Will that make the Brembos not fit on??
I have a set of brembos for sale you can try them on to se if the fit your wheels I checked caliper mounting and it is the same as calipers if you want to try them call me on 01628671056 or 07768356204