I am talking single step mash but I also sparge at 165. If I am sparing at a higher temp does it matter with the mash temp?
The sparge temp will generally inactivate any enzymes left in the mash too, so you'll get no more conversion.
If you mash-out around 170 F (hold for 15-20 minutes) you should inactivate any enzymes left in the mash (thereby halting any further conversion of your sugars, aka fixing [or setting] the fermentability). As long as the pH remains below 6.0, you should be OK if the mash-out temp goes above 170 F.
However, if you conduct a vorlauf and collect your first runnings into the boil kettle you still have not inactivated any enzymes in the wort that is in the BK until you turn on the burner and get the wort heated up well past 170 F. Same goes for the grains and wort in the mash tun--the 165 F sparge water isn't inactivating the enzymes (not quickly, anyway), so there's still some conversion taking place.
Now, factor in how long it is taking you to lauter and sparge. If it is 60 minutes of mashing followed by 60 more minutes of lautering and sparging, then you've got a different wort than if you had done a mash-out at 40-60 minutes. Both methods may make good beer, but it may be something worth considering if you're trying to make a sweeter, fuller-bodied beer.