Melees atm seem to be supreme.

Casters can do well, but they have to be smart. Demo's get a wicked root... root and then nuke till dead. Necros have swarms of pets that are lethal. Casting with three necro pets on you is damn near impossible.

The main thing about casters is planning ahead. Your spells are on semi long casting times (think x2 wow) so you have to plan 2 moves ahead.

Spellweaving isnt in beta and wont be till launch, its one of their secrets.

Your system should be fine, you might not be able to run it on max, but you will be able to run it. Its hard to judge performance at this point mainly due to it being beta, and 100's of people standing around you. I dont get any performance issues in the actual arenas.