Temps, power-draw and noise
The one distinct advantage the Radeon HD 6850s have over the HD 5850s and GTX 460s is with respect to power-draw.
Noise
Two card are obviously louder than one. Putting in two reference HD 5850s and comparing the noise profile to the GTX 460s and HD 5850s, the odd one out is the older-generation 5800-series which, when run in two-card CrossFireX, can be clearly heard from within a Corsair Obsidian 700D chassis.
The newer GPUs are quieter in both single- and dual-card setups, to the extent that neither the HD 6850 nor GTX 460 are particularly loud when running card-frying FurMark for 15 minutes.
