If you search old posts by Paul or Rick (the original KX500 masters) you will find the clutch cable reroute mod. Essentially you reroute the cable so it stays on the clutch side of the front downtube. You have to put the stock metal bend in a vise and carefully "unbend" it a bit - which makes the pull easier. If the 450 cable fits, and has less bend it might make that mod even easier. Who want to test that and report back? Could be a nice enhancement. My KX500 clutch pull with the 8mm extended lever, the cable mod, stock lever, and DP clutch springs (a tad springier than stock but about the same pull) is about the same as my 450, so it can be done. The overall action is better than my 450. I never felt a need for the magura setup on the K5 since I have never used a KTM one that I completely liked. But then I was bummed when my CBR900 didn't have one. Cam.
PS for someone with poor clutch action the fingers of the clutch basket could be grooved, which prevent the plates from sliding smoothly. Bikes with lots of miles can get that.