My PC is specced as follows:
16GB DDR3 (4x4GB; same manufacturer and model)
ATI Radeon HD 5770
I have all graphics options set to their lowest possible settings. I play full screen at highest resolution.
What I generally see in MP games is that, when we begin fighting an elite group (could be the first, could be the 20th), my FPS drops to a point where the game sits at the same screen for 15 seconds and then advances one or two frames and then freezes again for another 15 seconds. At the same time, I hear a fan (I am assuming the GPU fan) slow down. Eventually, the lag goes away or I lose my connection. Usually, when things get back to normal, I am dead. One time, I accepted resurrection, and started running over to the Legendary that had dropped, and was disconnected from the server! Yay! Oh well,...it was probably just a brimstone anyway!
This does not happen in SP games. I can play SP games for hours on end. I can play Borderlands 2 with no issues. In fact, I can think of no other app that ever crashes on my machine. (Well, IE crashes sometimes, I guess!)