I have a rc10gt and four x cellerators. They are both very good trucks.
To tell the truth I like the x cellerator a little better. Like they said on the X cellerator fourm,
the only weak point is the rear hub. If you spend the money right away and install the alloy rear hubs you will have few problems.
Many of the losi parts fit on the xc.
If you live close to a hobby shop that you like you may be better off with the gt. One of the main reasons that I like the xc is that I can get parts Very quickly online. I have to drive over an hour to get to a shop. All shops have parts for the gt and from what I understand only shops on the west coast have parts for the xc. Still, the xc is a very good truck. I have had very few problems with the pro kit, the rtr has a crap radio. I have only broken front and rear hubs on the track, Bashing on the other hand, anything can happen.

Either truck is a good choice depending on what you want to do. Remember, these trucks need alot of attention. It is a good idea to stock up in suspention parts if you want to keep going.