I agree about staying away from the Kawasaki Ultra 250/260. To many failure stories with those skis. But there is nothing wrong with a 2 stroke. My recommendation for the OP would be a late model Yamaha GP1300r if he wants a fast ski. He could get a really nice 07 or 08 model for $6 grand. Or a used RXP/RXT would be a good choice too.Ok, two strokes are old school. They are more expensive to operate. They are very inefficent because of the nature of a two stroke engine. You have to worry about oil injection and carrying expensive injection oil. They put out way more pollution than 4 strokes. They don't last as long and foul plugs.
The 2007 Ultra 250 are notorius for complete engine failure due to poor crankshafts. They are known in general for poor reliability.
If you want a bullet proof 4 stroke get a Kawasaki STX 12/15f I heard only good things about those skis.