Many X58 boards had a sort of "QPI Degradation" to them, but it was unrelated to temperature. As QPI approached 4GHz (BCLK at 220), the QPI (link between X58 Chipset (which handles PCI-E lanes) and CPU) would stutter really badly and cut 3D frames massively. This is why QPI Slow Mode was useful for 2D but not for 3D.
I uploaded this a few years ago while messing with my RIIIE: