I have never ridden a 450 Rebel, or even a 450 Honda, but I did have an '81 Suzuki GS450L. It had WAY more power than the 250 Rebel.
But I still see the 450 Rebel and the 250 Rebel in completely different ways. I see the 450 as a collectors item that almost no parts are available for. If I had one, I would rarely ever ride it, because eventually it would break down, and with no parts available, you couldn't fix it.
On the other hand, the 250 ('96 and newer) is cheap, plentiful, all the parts are readily available, and it makes a great beginner bike, transportation bike, or as the starting point for a custom. I bought my '04 completely stock, and have been slowly customizing it for almost a year now, one piece at a time, with no plan. The only requirement is that it remain a practical, functional motorcycle, which rules out a chopper or bobber. Jerry.
I get a little over 70mpg on my 250. All original parts minus what i've repaired, maintained and kept in tip top shape. it is, however, too small for me. I am 6'1" and so it has mostly served as a backup vehicle or a loaner.