The 420 is the great grandfather of the x750. It is everything you are going to want if replacing your 420 is the goal.
If you really want the ultimate get the x758 for the hydraulic all wheel drive which is just an awesome upgrade over plain old boring 2wd.
If you want a gas powered option which is a great option the x738 or x739 are just as good. The Kawasaki EFI liquid cooled engine is everything you want out of a gas engine option. The x739 adds 4 wheel steer in top of the awesome AWD.
If you really want the ultimate get the x758 for the hydraulic all wheel drive which is just an awesome upgrade over plain old boring 2wd.
If you want a gas powered option which is a great option the x738 or x739 are just as good. The Kawasaki EFI liquid cooled engine is everything you want out of a gas engine option. The x739 adds 4 wheel steer in top of the awesome AWD.