Here is my experience, i've buy a 400 exc 2002 and plate it as street legal, i've buy aggressiv tire kenda trackmaster cuz i wanted dot legal... i have discover in 4 months of riding, that a bike cannot be good for dirt and road at the same time. first reasons why are tires,a lil use trackmaster arent s12 in mud and trail, it means i had more difficulties in trails and i didnt get much on the road cuz i didnt want to scrap my tires... and a s12 on road may do around 300 miles and thats write on it NOT FOR HIGHWAY USE! they are kinda dangerous on road.
Man keep your wr426 and buy a street bike you'll save money. Dont think you'll be happy to get out of a muddy day and get back at home all wet melting your new tire, think about it, a trailer or a carrier is a better thing!