Originally Posted by barrier911
If a 300 KTM is close enough to the 450's in terms of torque etc we would just be left with comfort and fuel range.
Having just come back from a few weeks of beating my 300 and 530 around the desert, I have an even fresher perspective on this than usual.
First, engine performance. On paper, the 300 and 530 aren't that far apart in terms of peak horsepower, especially when you consider the lower weight of the 300 as compensating for the few HP it gives up. Torque is not even that far off.
But, in the real world, they are miles apart. The 300 makes something approaching peak torque for just a couple thousand RPM, and is relatively weak elsewhere (this weakness is what people call "tractable" and makes it a real weapon in technical situations, because you can short shift it and it doesn't light up everywhere). The 530 makes great torque over a much wider range of RPM (aside: it is also great in the technical situations because it delivers that torque so subtly if you have good throttle control. The 300 really doesn't, it's a bit of a light switch, and you need good clutch control and to be in the right gear to get the best from it).
I haven't looked at a Dyno on my bikes, so take this with a big grain of salt... and jetting, exhaust port setup, and pipe choices can make worlds of difference, but if I had to guess, I'd say the 300 makes peak HP at something like 8K RPM, but doesn't really start pulling HARD until 5-6k, and runs out of steam shortly after it maxed out. It has useable torque below that, great torque for trail situations, but if faced with a big heavy rally bike trying to get max accel out of a turn, it would be underwhelming outside that band.
Furthermore, it comes on pretty hard and abruptly, relative to a 4 stroke. So it's not as easy to pitch and drift and slide on fire roads- it certainly can be done, but nowhere near as easily as the 530.
The 530, on the other hand, is incredibly smooth in how it delivers torque, making it easy to ride hard, and delivers useful torque from probably (again, a guess) 3000-9000 RPM. That's a band 3x as wide as the 2 stroke, even if the number isn't that much higher, it's a hell of a lot easier to keep the thing roosting forward.
Then there are the comfort elements of vibration and so on. My 300 is pretty smooth relative to the other open class 2 strokes I've ridden, but you start hating life not very far into a fire-road section, unless you are caning the bejeebus out of it. Then you're afraid enough not to notice the vibration. :-) That's not how you race a Rally, though.
Finally, with regard to maintenance, the 300 will go a bazillion hours without batting an eyelash in the hands of mortal riders, because they are generally in that underwhelming part of the torque band where trailriding actually happens. Start spinning it for hours on end at the torque and HP peak, and that story will change in a hurry.