John,

I've never seen one of them composite Q500 planes fly... but I'm pretty sure a good Magnum is faster (on the straight).
We fly woodies in Q500 over here... but a good woody is still a very fast plane. And the Magnum is considerably faster.

The one time I had my Magnum measured, it was doing close to 140 mph on a shot engine. It had thrown a part of one of the piston pin retainers and had three huge scratches running along the cilinder wall and piston. The engine had NO compression what so ever... it felt like there was no plug in it when you turned it over... impossible to hand start.
Needless to say, it was a lot faster on a healthy engine