As you probably gathered from the individual data tables, the MCW80 takes the crown for being most restrictive followed by the Rasa GPU. .. the older block is extremely low in restriction, while the newer MCW80 has more restriction than it should. If you running more than one GPU with MCW80′s in your loop, you either have an extremely low flow rate or you are compensating with several pumps in serial. To put it another way, with an MCW80 and a D5, you cannot achieve over 1GPM, even if your loop does not contain any other components… Yes, the MCW80 is that restrictive.