AMD PHENOM II 955 TO i5 2500k

No. You need at least a new mobo + CPU which will run you around $270-300. Games do not utilize 4 cores and most games are bottlenecked at the GPU. Upgrading your GPU or monitor is more noticeable depending on what resolution you play at.

WHy is your mem not compatible with your standard 240 pin/DDR3 based MB?

http://www.asus.com/Motherboards/AMD_AM3/M4A785TDV_EVO/

Until there is some sort of gain with >4 cores during gaming, you would primarily be gpu limited at 1080P or above anyway...

The 6870 is roughly equivalent to most GTX560's , solid enough, IMO....

Yes a 2500k would be a pretty big boost from a 955, but is the 955 too slow for you now? Realistically if you overclock a 955BE it shouldn't hold back a single 6870 or even dual 6870s IF your using eyefinity. As for upgrading to a 6core CPU it really isn't worth it for gaming, most modern games like more than two cores but don't benefit much beyond three, but if you spend a lot of time encoding videos or something then it's something to think about.

Anyway, it depends on you and what games you play. If your setup is enough for you right now, then I say wait till the fall at least. Bulldozer will be out soon and even if you go with Intel they will probably drop their prices a little to put pressure on AMD. Their high end LGA 1366 replacement is also around the corner  

Memory is OCZ3P1333LV4GK Platinum and it blue screens at default and at 7-7-7-20 @ 1.65V

http://www.ocztechnology.com/ocz-ddr3-pc3-10666-platinu...

The OCZ memory above worked fine on a BIOSTAR MCP6P3 and that was just using default settings. So i dont think the memory is faulty.