The difference is which bikes faster because we race people in the neighborhood and want to know how bad I would smoke them
Questions like this tend not to be well received by people who spend a lot of time with dirt bikes for a couple of reasons. For one, none of the bikes you listed were ever built as drag racers, so where any of them would beat the other is something that the manufacturer never cared about while building it in the first place. That in turn is because most of the people who use them for their intended purpose don't care about drag racing, either. They're built for racing on an MX course or in the woods or deserts, where cornering, climbing, descending, and generally handling rough terrain at speed are skills at a premium, not drag racing. Certainly, the ability to accelerate hard, even from a standstill, plays a part in these pursuits, but only a part. Any reasonably good racer will be able to tell you that he's beaten lots of people over the years that were on more powerful, quicker, faster bikes than his own by playing superior skills against them in places other than on the straights.
Of the 3 bikes you listed, the 426 has the most power and the most gearing in stock form, giving it a significantly higher top speed. The '97 is actually apt to be a bit less powerful than the 250F, but if you can't launch the big bike, or control it well enough to find traction with it, either one may well beat you. And again, not many people here care about the winner of a drag race one way or other. It's a little bit like comparing the length of one's genitals to establish who's "better". I would, for example take the 250F out on an MX or desert race course against you on your 426 and probably hand you both your back pockets, and then you'd have been beat by a bike with at least 7-8 less horsepower, one that would or should never win a drag race against the bigger bike. Thus the question, "what difference does it make?"
The other thing is that it's an obviously "newbie" question, if that matters.
FYI: a power band is not a part.