Hello, I've got a question about whether to use panniers or a cycling backpack for my commute to and from the train station near my college (8 miles each way):

I carry two large volumes and a 6 pound laptop daily on this commute, which I have to get through in at the most 40 mins.

Would a pannier (convertible to a backpack if possible) or a cycling backpack be better? I don't like using the backpack because its stiflingly hot out here, and I will arrive at class drenched in sweat; however I don't like using the pannier because it changes the handling of the bike, and it's kind of a hassle to take off the bike when getting on the commuter bus back home.

Can anyone recommend a good backpack that will keep the weight off my back so I don't sweat as much, and/or a pannier that can be removed very quickly and converts to a backpack?