I had a 4870 (Well, Crossfired 4870's) all through 7 betas and the entire Alpha, Ant. And I have to say I never ran into the problems you did during that time. So your issues are probably uncommon, perhaps your card is going bad?
And Cutter why don't you stay out of these Rift threads with your F2P comments, we all know by now you want single player MMO's that you can quest through alone and then quit. Sorry, not going to be the case for this game. Lots of guilds have transfered in from WoW, Aion and Warhammer due to the beta. They have a ton of servers that are already filled to the brim with queue times and have been slowly opening more.
It's the largest release I've seen since WoW. And I played Aion and Warhammer at release, so I can compare quite easily.