My first bike when I got back into riding was a 99 YZ125 and now I own a 01 KTM 200MXC. Go figure.
The stock forks on the 200 are a bit harsh for woods, but they might well be just the thing for track after you break them in a bit and fiddle with the oil.
As far as engines go the 200 is clearly stronger and has a more predictable powerband than the 125. With stock gearing it will pull a wheelie in 2nd and 3rd without provocation, is capable in 4th and will dig a trench in 1st if you are not careful. It is still a small bore and you have to row the box to really make it sing, but I have to say the 200 is at least twice the bike as the 125 I had.
As far as comparing the 200 to the YZF, it has been a while since I have been on a YZF, but it is clearly a different bike, if only because it is a 4 stroke. They ride different and for me at least, I never really got used to stearing a bike with the front end (4 stroke) vs. rear end (2 stroke). I guess I am too old to learn new tricks.
If you race, you should look at the 250 SX if you are serious, so you will not be giving up 50 CC to everybody else in the class.