well, there is nothing wrong with your CPU, or PC for that matter. When the bitrate jumps through the roof it's either because your CPU is not good enough (which in your case is not the issue) or the network just simply can't handle it. I had 100Mbit wired network at home before, and when playing 1080p movies the network couldn't handle it, and the bitrate went through the roof. Changed to Gigabit network, and everything worked perfectly. I think it's safe to blame your wireless, if 100Mbit wired network isn't even good enough, then I think it's safe to say that it is your wireless network that is the issue, not the PC.