Got a quick blast on the 450 yesterday and was very impressed.
What I noticed straight away:

Suspension was softer but still well controlled. Sat a little lower.
Power was very close to the 520 lower down and mid, but just a little behind in the top range.
Riding position reminded me of the DRZ400.
It looks superb in the flesh. Big hub's, gold frame and 'no seam' seat all set it off.

Both lad's on our run love them!

Glad I ordered as the waiting lists here in the UK are a joke!