I had a 2000 KLX and now have a 2003 WR250 The WR will eat the 300 alive.
Starting is one of the best things about the WR you really don’t need the electric start, it kicks soooo easy, the KLX you still need to find top dead center. The good thing about the 300 is that it’s a 6 speed and it handles really great, almost as good as the old 02 Gas Gas I had.
It’s just not a race bike with out throwing money at it while the WR can do both(just putt or scream) stock. The KLX is almost unchanged since started out as a duel sport 250 in Japan. Hope this helps.