So after driving over 500 km on city streets, highways, windy country roads, gravel roads I've come to a verdict.
I guess the best place to start is to talk about the tires I used previously. I had the stock Yokohama Geolandar G96B tires in P245/60R20. They had about 45% trend remaining so they were still in pretty good shape. I can only compare the Coopers against these tires because its all I know.
New Tires: Cooper Discoverers AT/W 275/55/R20
Handling
The Coopers are definitely better in the handling department. I feel more in control while driving at high speeds, easier to keep the car straight and while turning the tires hold the road very well. There's this stretch of highway I always drive, the speed limit is 110 km/h, its downhill, there's a bend in the road and I usually gas it to get momentum for the upcoming hill. With the Yokahomas I always felt uneasy driving this stretch, I always felt the car was on the brink of rolling over. Doing this same stretch with the Coopers felt much better, felt comfortable the entire way.
Gravel Roads
This was a massive difference. The Yokahamas totally suck at gravel roads, I normally drive around 60 km/h cause anymore I feel the car loses too much traction (speed limit 80 km/h). I was driving comfortably at 80 km/h and felt I could do another 10 km/h no problem. Another difference was the comfort of the ride, it was very smooth, surprisingly smooth (this could be due to the higher speed 60 km/h vs 80km/h). Bottom line the Coopers performed much better than the Yokahamas.
Mileage
So far the mileage from the Coopers seems to be the same or better than the Yokahamas, which is kind of surprising considering its 245 vs 275. The difference could to me driving differently, breaking less going into turns or because my tire pressure wasn't optimal before. So if you are worried about the fuel economy of the 275s don't be cause there doesn't seem to be much of a difference.
Noise
The Coopers are definitely a lot quieter than the Yokohamas, my girlfriend and I both noticed this right away. While driving in the 80 km/h - 120 km/h range we were able to listen to music at a comfortable level. We normally have to blast the stereo to hear anything.
Turns were a huge difference the Yokohamas seem to squeal all the time, even in the easiest turns. Haven't heard a peep from the Coopers yet.
So that's my limited review of the tires. I wish I could have reviewed them in the rain but it never rained over the weekend. I expect these tires to perform superbly much better than the Yokohamas. I've had some scary hydroplaning moments with the Yokohamas and because of that made the change. Well hope this helps someone out. I'll keep updating after some milestones.