I'm not familiar with the JE kit. I had D&D (Pensacola, FL) do mine with the Wiseco pistons. D&D offers a higher compression piston instead of the Wiseco for the same price. I opted for the Wiseco. The first BB kits they did were with the Wiseco sleeves. They decided the bored and nikasil (like stock) was the better way to go. I don't know about the cooling, but it should last longer.
As Dave said above, you would have to put a LOT of miles on the bike to make a difference - you may never get there. I'm extremely happy with my bike now. Either way you go you will be very pleased with the BB result. I went for all the torque they could get especially in the middle range. That's why I opted to not go with the higher compression pistons. I wasn't just looking for maximum hp.
I even tried their lower mass flywheel but had them swap it back for stock. It increases hp at higher rpms but took away some of the torque at lower rpm when starting off. After all, we ride the bikes on the road, not on a race track. If you've got someone qualified to do the BB, do it. You'll never regret it and it's tremendous bang for the buck. My bike is staying the way it is as I have all the power I want even riding 2-up now.
