Bear in mind that when I say four-seasons it's a lot different than when tire manufacturers (and other cyclists) say four-seasons. To almost everyone else, the fourth season is rain, not snow. (For snow, I use Nokian Hakkapeliitta W106 studded snow tires in 35/38mm.)
As for the Conti GP 4-Seasons, it's the tread compound that impacts the grip. The rubber is just plain stickier. Construction and the use of a Vectran breaker instead of Kevlar is what does it for the ride. Handling comes from a little bit of each, I expect.
Don't forget, the bigger your tire, the lower the pressure. I run my 28s (on the wide 23mm rims) at between 60 and 65 in the front, and 70-75 in the rear. See
Tire Drop for details.
EDIT: The best pricing on Contis I've found in the States is from
TireManiacs.com. Their prices include shipping to the lower 48.
Thanks for the clarification and link (though when I tried to to there it gave me "server application unavailable" error). I have also seen these at a number or local shops, so might be reasonable to get them local particularly if I can get them with a bike coalition discount or something similar.
Any idea if the Vectran is as effective as Kevlar? I have been VERY happy with the flat resistance of the gatorskins.
I am thinking about trying a set of these in 28s for the winter and comparing the performance with the Gators on my current bike.
I knew that larger tires mean lower pressure, but I am curious as to why you run you rears higher then the fronts - is it as more weight is on the rear or something with handling? Maybe this answer will be in the Tire Drop link you provided, which I will try to read soon.