I owned an '01 KTM 450MXC and now have a '96 KX500. The KTM was heavier and felt TONS heavier. The ergos were a little thinner, and it was a little less effort to stuff into a turn... The suspenion is not MILEs apart like some people are saying.
If wheelspin is an issue for you on the K5.. then it's very likely that all ya gotta do is just click-up to the next higher gear and make use of that 500 grunt.
It's strange how some people on here are soo stuck on the concept that BECAUSE it's a 4t you believe it's faster for you in situation X, Y or Z.
I will agree that probably the MAJORITY of your average Joe riders can go faster on a 4t because the power comes on in a more linear fashion so they don't have to learn as much finesse and the fine-art of clutch work fishing for traction. And they don't have that yummy concentrated "hit" of power centered around a certain rev-range as 2t's are more usually prone to do.
Personally... I've found that the 2t style of power... and having much-less of the compression braking affect in the long run teaches me to ride faster. it's like you sorta are forced to learn how to enter into corners coming in hotter than you would on the 4t. I don't quite know how to put it.
And puh-lease!!!... ANY 250cc 2t can murder a 450 4t any day of the week.
Yeah... sure... if you put a total SQUID behind the controls that's not going to happen... but any reasonably competent Vet on a 250 2t will eventually slip past a guy on a 450 4t.
And comparing the 450 4t with a K5.. HA!!! There is just NO COMPARISON!
Phew... it makes me drool to try to imagine just how bad-a$$ one of that KX500AF's must be. Putting the K5 BEAST into a one of the new-style nimble, narrow frames.. now THAT would be something to BEHOLD!!!
As for why you are only seeing 4t's on the starting line at SuperCross events... DUH!!!! The companies are dumping all kindsa R & D money to go this 4t route since they fear the EPA eventually will stomp-out 2t's... not only that.. they know they can make a boat-load more money at the dealership with the increased maintenance service costs
I wasn't going to reply to this but in the end felt compelled to comment, and I might add that I have a 06 250 2t, 07 450 4t and aluminum framed 500, my son has raced nationals so he's no slouch on the track. The 500 is great in the wide open, hillclimbs, desert sand, the 250 is a fun bike trail riding, the 450 is a track bike, having said that there is no way equal riders the 250 will run with the 450 on the track, you can talk about finesse whatever, it won't happen. When yamaha came out with the 250f and the rest of the brands still had 2t, you had to have a better rider to compete with the 4t, on a local level mediocre riders purchased 250f's and all the sudden became top level riders. There are some tracks where a 250 can do well, momentum tracks like Mammoth Mountain, but it seems there are a awful lot of slick hard tracks out there and the 250 won't do it .
I might ask what you basis for comparsion is? do you have these bikes? or are you just assuming? Don't get me wrong I like them all, but they are purpose built machines. Maybe in the Vet class and even beginner classes the 250 can be competitive, not in the Pro class.
I don't like the KTM suspension, so your probably right the 500 and you 01 450 were probably not that far off. Nothing personal to you KTM owners, that's just my opinion.
One other comment, I think I like the 500 in the 05 250f steel frame better than the 450 aluminum frame, it feels much smaller and seems to handle better, can't quantify that just going by feel.