That's too bad you've totally written off trying out the darkside but to each his own.
The Avon Cobra I now have on the front was an improvement over the Metz in a couple areas that I noticed right away. It handled crisper, the bike WANTED to turn where the Metz fights it a little. The ride was smoother and less jarring over road seams. The Avon is wearing more evenly than the Metz, the Metzler began to cup on both sides almost overnight where the Avon hasn't changed in 7000 miles, in fact it still looks new.
Pete.Triumph's comment about it being dangerous to use anything but OEM is silly, vehicle manufacturers are more concerned about cost and availability over performance and safety. They use the best tire they can based on cost and work a deal with the tire maker for price and a dependable supply.
Each tire is a compromise, they obviously cant all perform the same function the exact same way another does. So you make choices based on what is important to you and how you ride it. Any Darksider will tell you that riding on a car tire is a compromise, it's not perfect. But to us the benefits far outweigh the negative quirks, I'll be the first to tell anyone who asks that they have a tendency to follow ruts in the road at slow speed but the 240 Metzler did too. Car tires have more mass and increase the unsprung weight a little, but the Metzler was so thin that it wears out quickly. The Metz has no tread at all in the center of the tire and hydroplanes easily where the car tire has tread and disperses water with ease. Running 40psi in the Metzler makes it a brick and the ride is harsh compared to a car tire with 28-32psi.
Tires are as personal to the rider as a pair of shoes, you can't expect golf shoes to perform well on a basketball court ... you have to decide what you do more of or buy multiple pairs. Right now I'm loving my BFG/Cobra combination, the compromises are hardly noticeable to me.
So if the tire fits, you must acquit.