Just wanted to give an update. I ended up getting the 28mm gatorskin hardshells. I had a gift card and a 15% off coupon so I said hell with it. They fit on the bike and everything seems ok so far.

I've only gone about 40 miles on the new tires. I haven't noticed much of a speed increase yet but we'll see after biking this week. I did notice it is easier to get going from a complete stop.

Don in Austin,
How long did it take you to finish that century? I have a feeling I can finish one with the current bike, I'm just going to have to go at a comfortable pace which will make the ride longer. I have gone fairly decent distances before. I've done a 50 mile tour and the most we've done in one day was about 64 miles. I noticed my hands do go numb after awhile. I bought some Ergon grips to replace the stock grips and they have helped a bit.

coldfeet,
I've heard good things about the Schwalbe Marathon Supremes but the local stores didn't have any in stock. I didn't have much to choose from actually lol.

I think these are the last upgrade i'll purchase for this bike. If I end up trying tours more often I think i'll look for a new bike.

Thanks again everyone for all the help and advice!