Last week I put Titan 589 27x11x12 rear and 26x9x12 fronts on and they are great. I could not believe the amount of traction these tires get compared to the stock 489's. Places I always had to use 4x4 to get through I can get through in 2 wheel drive without slipping a tire.
Now you are probably wondering how much power I lost. I wondered the same thing while I was waiting for them to come in, even lost some sleep over it. I saw were Boner had posted he had a friend that had 27/26 setup on a 300 4x4 and it did fine. Thanks for that post Boner, thats when I decided I would try it. Well, it pulls those tires just fine. I lost a little snap, probably due to the weight, gained 15lbs. on each rear and 10lbs. on each front for a total of 50lbs.
As far as I can tell I top out the same about 43 mph. Speedometer reads 40 mph and I figured it read slower due to the taller tires. It did take a little longer to get top speed and I can pull 5th gear in high.
Now for hills, and I use that word lightly because I live in IL. I can take pretty steep slopes in 1st gear high as long as I keep my speed up. If I go slow and loose rpm it is all over. I can also go in sloppy mud in high. I have not found any real good mud holes to try it out in yet. The deepest I have on my property is only 10" deep and soopy.
I have used middle gear and 4 lock for some very steep inclines. All 4 tires just grab and go. The front end does not seem as light as it used to be due to the extra weight up front which is really good for steep hills. I have flipped mine over backwards once and have rolled it once down a steep hill. It was no fun. With the heavier tires the front sticks to the ground. I have not needed to use the low setting yet. It is very very slow but tons of torque.
I have jumped it some to see if was going to bottom out anywhere and it does not. They were small jumps, about 3 ft. of air but that is all the higher I would jump a utility quad. I gained another inch of ground clearance so I have 10 1/4 total now. It also clings to the sides of hills like glue. I guess this is because of the extra weight of the tires.
Anyway, I am very happy I chose these tires and would recomend this setup. It also looks mean as heck!!
Later...

 

Copper thanks for the info. I too have been going round and round about what size tires to get on my AC 300. Your post has made up my mind. Thanks for the information, and good riding.