I have a 2010 Mac Pro dual processor into which I put a genuine 4870 from my 2009 Mac Pro. Today I installed a brand new Inateck KT4004 into slot 4. When I plugged a USB stick into it it took 30+ seconds to mount. I thought this was odd, so opened System Report to have a look. When I checked out the PCI section I saw that my ATI 4870 had a link speed of 5.0Gb/s but the bus width was x2, and I presume that it should be x16. I didn't have time or the space to try moving the card to slot 2 and seeing what it negotiates. Does anyone have any idea what could cause the card to negotiate a lower speed with the GPU? Is there anyone running a 4870 in a 2010 Mac Pro? Does it negotiate at x16 or x2? According to Apple, the 2010 doesn't "support" the 4870. I'm wondering if the x2 is because the 2010 isn't reading the 4870 properly. I've had a few random problems with this machine (shutdowns out of the blue). I've run ASD on it and it comes back pretty "healthy" except for a temp sensor issue on slot 1. I've read on another forum that this is because the 5,1 isn't compatible with the 4870. Tomorrow I'm going to swap in a 680 GTX from my 2009 Mac Pro and see if it negotiates x16, to rule out a problem with the backplane board. I have an Inateck card in my 2009 that I'm also going to swap into my 2010 to see if the new card is "broken" or whether it also indicates a fault with the 2010. Anyone have any thoughts?