Well, for the math challenged, it's really 10mm if you compare it to what he's currently running on his MTB (175). And from the little info provided I'm going to assume he's talking about building an SS MTB, not a road bike. And I will say this, it's a lot different ball game cranking an SS MTB up a steep singletrack hill than it is cranking a fixed gear up a steep paved hill. Most people will notice a 10mm difference. Just for the hell of it, do this: drop your seatpost 10mm on your fixed gear and ride for 20 or so miles and see if you notice it. I bet most will.

All that said, just try the cranks. They are bought and paid for and you haven't stated your height, so they might be right for you anyway.