Honestly, you need to test ride and find a bike that will fit you... If it happens to be a trek, that's good... But there's a lot of other great brands of bikes out there. They're the giants, specialized, etc. And... you're not going to ride a bike if it doesn't fit you well.

So test ride as much as possible...

Shimano 105's a good drive train source - shifts well and will last. I think you might want to test ride some aluminum frames with carbon fiber seat stays to compare with the straight aluminum frame of the 2.3. You might also want to test ride a steel bike (look at the jamis bikes). I find aluminum a harsh ride even with a carbon fiber fork - if you've got a lot of chipseal around you, you may not want aluminum... and if you're talking about doing a century than maybe you want something a bit more comfortable...