I have both and I don't think you can compare them against each other. The Speed 8 is the smoother ride, but with only 8 gears a bit limited to what you can ride. The P18 is a full road bike, ride almost anywhere. I think the P18 should be compared against the MuP24, which I also have. I'm not a fan of the Dual-Drive system, too noise in middle setting and the Mu frame hits my heal when I pedal. If you are just riding in an urban setting the Speed 8 is perfect, if you ride long distance in the country the P18 is perfect. Best yet, buy both!.
thank you where much for the answer.
Fun to know that someone having a Vitesse P18
I riding from work 2-3 times a week its 33 km one way.
I really think Vitesse P18 is perfect for me due to I find the Speed P8 is missing gears for road/parvel ways.