Not really sure about a 440 ex but I have a friend that has a 416 ex with cam, port & Polish, full pipe, air filter, CDI Box, 39mm FCR Carb, All of that junk. It actually runs decent But still no match for a ported Banshee. My banshee is pretty much stock except for pipes, Ported and cool head and I can beat him by about 3 bikes in 300 ft. and just keep pulling on him. He is about 1 1/2 bikes behind a stock 450.
A 400 ex motor is just too outdated. I think instead of changing the plastic they should have updated the motor instead. Atleast to try to make it run with a z400.