Chains
 

Although I'm not sure, I think my 1600 was rocking a 105 chain today when I completely snapped it in half. Now, my Trek is only 3 days old, and shouldn't have wear on ANYTHING yet. Luckily, my LBS replaced the chain for free, but I've started looking into Dura-Ace chains. I'm wondering if the 10spd one will fit my 105 cassette/shifters. Will it?

Also, will the shifting be any smoother? My (105) front derailleur has trouble shifting under high chain tension..... Which is why I'm also looking into a Dura-Ace or Ultegra front derailleur.

Take this opportunity to look into wipperman chains with their easy to use master-link for great cleaning. 10spd chains work with 10 spd systems.

The 105, Ultegra and DA chains are all the same except for a wear resistant coating on the DA chain. Otherwise, they are all the same, with the DA chain actually being slightly heavier, if my memory serves me. Your chain snapped because of a (more than likely) improperly installed pin on the part of the shop, or a random bad chain, which happens in any manufacturing process. I've had the highest-end SRAM 10sp chain snap on me, as well as a DA, but not a 105 or the middle of the line SRAM chain (those were replaced due to wear/stretch).