RE: Is the CEN matrix pro kit any good?
Well the CEN Matrix sounds just perfect for you. It's a very durable kit, and at the perfect price range. As you can see, it competes with the best of them, and parts probably aren't going to be hard to get. The best upgrades to get are probably the front CNC steering knuckles. The stock ones are sometimes easily broken, and they inhibit steering capabilities. The rest is really as you want or have money for. If you plan on racing, the top upgrade/conversion is the BCE chassis conversion. It changes the geometry slightly, and it makes the truggy much lighter. It is not a necessary upgrade though. More so for the hardcore racers.
The GST 7.7 is a huge truck, but I would recommend getting the Nemesis 7.7 instead. It has a stronger driveline and differentials. It is also lighter, contributing to the durability. The only things you don't get is a third speed and reverse. Think of the GST as the Bentley will all the bells and whistles, and the Nemesis as the Dodge Viper..hardcore and utilitarian.
Good luck with your choice. You can't go wrong.