"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."

difft situation though; certainly leg extension is critical to efficiency/comfort...but leg extension is adjusted relative to the bottom of crank i.e., if your running 165s, your seat should be approximately 5mms higher than when running 170s. much bigger impact to the larger scheme of things than cranklength.

here i go...overanalyzing again...

just ride.