I used E3's on my Shadow Tourer. The front was Goldwing and the back was Valk. and I tried a GW rear tire once. I averaged 8000 - 10000 miles on the rear and got up to 18000 on the fronts. This was on a 625 lb bike and I weight in at 280. I really like the stock F6B tires so far, and 19k is impressive too me for bike tires.

As far as the dark side, I have not tried it, but the people I ride with who have, swear by car tires on the rear. I've been offered to ride a friends GL1800 with a CT, but have not yet.

Mike