Should be easy to find with a bit of searching, someone posted a detailed guide on how to do it for both internal and external PSUs. Edit: Actually, I guess I haven't posted links to the discussion of how to rig up an external power supply yet. Links in my FAQ thread with more details. More power to you (no pun intended) if you want to ignore our warnings and run with a converter cable, but our standard advice for anyone using a card that has one or more 8-pin connectors is to drive it with an external power supply. People have damaged their cards by trying to make an 8-pin connector work by using a 6-pin to 8-pin converter, trust me this has been discussed at length in many different threads. You're pulling up to 150W from one of those cables, which is not in the 300W budget for all PCIe slots, it's from the separate connector on the motherboard. The second cable provides the final 75W for a total of 225W for one slot.
That's 300W across four slots, or 75W per slot. They tell the graphics card it's ok to draw 150w - which it is. So those two extra pins are grounds only. Pins 1-3 are hot, 4-6 are ground + 7-8 ground. The 6 pin has 3 grounds and the 8 pin uses 5. In fact, the only difference between a 6 pin and an 8 pin connection is the number of grounds. However, it's not exceeding the design spec at all. Not sure why you're suggesting I'm not aware of this. I'm not fighting with my graphics card here. Something a little more 'novel' for desktop solutions. Much more similar to a mobile graphics card would to conserve battery-life and manage heat. Also, while the Tahiti 7xxx cards do throttle, they do so to keep temps down while you browse the internet or other mundane tasks that don't require full-draw. I suppose there's nothing wrong with a little level-headed consideration and people should be aware of these things, but in this case, it's unwarranted. Your hard-and-fast ruling is just inaccurate, sorry. We're not putting the LB at risk with this setup. We're not overdrawing the lane and we're well within what's needed from the PSU. *Edit: The reason I keep pointing out the PCI lanes are 300w combined, is because that's how the LB is wired to power them as a 300w lumped together channel. GCN ArchitectureThe Radeon HD 7850 boasts revolutionary new GCN Architecture which is optimized for gaming and compute. There is nothing unsafe about running this card either. The XFactor - See the XFX DifferenceBuilt with the first class components including solid capacitors, ferrite core choke, dust-free IP-5X fan and XFX bracket design, this card delivers unmatched reliability, stability and durability even under the most demanding environments. We're not exceeding the LB or the PSU or even uncomfortably close to it. The MP has a limit of 300w across the 4 PCI slots and that 8-pin adapter does, as you said, allow the card to pull down more watts.