how many miles
I seldom keep tires past 25,000 miles. I live in a high snow area as well as the I-70 corridor so do some high speed driving. I've had different brand tires over the years on SUVs and am particular about checking tire pressure.
I find that by about 25,000 the siping on the edge of the tires has usually worn quite a bit. That is the area that gives you grip when turning on slick surfaces. Having worked in EMS for 30 years I find that good tires are the cheapest insurance you can buy. Why risk yourself, others, your vehicle, and peace of mind for $800 every few years? When the weather gets bad unexpectedly it is too late. I usually try to buy new tires going into the fall season so I'll get at least two winter seasons on my tires. I switched to the Revos from the Dunlops on my 06 Sport and will report mid winter on how they are doing.