The SXR was the pro senior...the race model before the senior adventure came out. It was relagated to the adventure title whent he Pro SR came with a Liquid cooled Beta motor.
The air cooled Morini motor that is used in that bike puts out close to 9 hp when properly tuned. It should be more than enough for a 5 year old. The clutch hits fairly mild but can be upgraded. If it has the 2 shoe clutch it can be trail ridden fairly decently. The Older air cooled Cobra's used the same Morini motor and our son rode for hours with just enough time for filling the tank. They are designed for the track but are good learner bikes.
What are your plans for the bike? Just something for your kid to learn how to ride on around the yard and occasionally at the track or possibly the trail. If thats what your looking for then I'd say jump on it. That is a decent price. I sell the 2000 air cooled cobra's for closer to $1200.
If you do buy it check out
www.egracing.com he specializes in the KTM morini motored bikes.