i find the dual discs are more a want than need personally for the slower things. my m600 with the single never had the big bite that i like so much, but it wasn't a technical issue as such.
as an aside, i find that the bikes that typically have the most front disc wear are our learner monster 659 (destroked 696). even with dual front discs, the young guys are either hard on the throttle or hard on the brakes. i've seen a few with undersize discs at 24,000km.
know all wanker