I ran mine @ 1.9v on stock cooling, there is a thread @ xtreme where someone did 2.1v on stock cooling for an hour and tons of people run @ 1.8-9
Now that's stupid, but they are NOT as fragile as everyone thinks. The early week ones were, but the later weeks memory controllers dont die nearly as easily (however they also dont clock as well).
I'd say if your temps are in control, 1.7v is perfectly fine 24/7 on stock. But watch the temps.