I don't know if you want to put any stock in what a magazine says, but Dirt Bike has a write-up (April 2003) which compares the 426 and the 450.
The main things they said which were better on the 426:
Gas tank is reduced from 3.1 gallons to 2.6.
Cannot adjust to YZF spec cam timing.
450 feels a little top heavy in tight twisties.
The new seat-tank junction undoubtedly allows you to be more aggressive.
And I think even with the magic button it weighs the same. IMO, you certainly won't be worse off with the 450, and the e-start will be worth the extra $$$.