Yup, the 2005 KX250 is a rocket with great legs right out of the gate. I wrote a first impressions post about a week ago, so you might want to take a look.
We actually looked at getting Ben a KX250F, but after testing a stock '04 against his almost stock '02 125, we found the KX125 was faster in the desert, less weight, easier to repair, cornered better in the trees. My thought was that if an '02 125 with almost stock motor was faster than the 250F, then the new 2005 KX250 should just eat the 250F's lunch. I was right...
In offroad racing, the 250F must compete in the 250 class against the KX250. While I can see the 250F competing with the 125, it just doesn't stand a chance against a two stroke 250. While the 250F is a good bike, it's just not in the same class as the KX250.
Before you toss any money into the '04 250F, might want to take a look at an '05 KX250. Either way, you get a Kawasaki, so can't go wrong.
Rick