Strange 5770 Wow and You Tube

Hey all,

I got a Sapphire ATI 5770 graphics card using the newest version of CCC (catalyst control center) software. I have a AM3 Rana 3.0 Ghz overclocked to 3.6 Ghz on a Gigabyte motherboard. Using the CCC AMD Overdrive I have the video card overclocked to 900 Mhz and 1300 Mhz (from the stock 850 Mhz and 1200 Mhz). The overclock is stable and has been extensively tested....now here is the problem. I play Wow pretty much 24/7 and when i play Wow and then play a Youtube video at the same time, the card goes to 400 Mhz for the GPU clock and 900 Mhz for the memory...weird huh? When I hit defaults and then hit apply using CCC, it still remains at 400 mHz and 900 Mhz. Only way to get it to reset is to restart the computer. Any suggestions WHY this is doing this and how to fix it?
Also was thinking of replacing the video card for Wow and Rift...debating between a 6870, 560Ti, a 6950 and a 6970....any thoughts on that would be greatly appreciated as well. Thanks in advance for all you help!!