300W sustained is a hellacious pace. Olympic caliber rowers can pull over 1000W for a few pulls. Crossfitters use either calories (this will count as a "rep" in workouts like Fight Gone Bad) or leave it set on the 500m pace. There are some excellent videos on rowing form at the Crossfit site featuring a chick who use to row in college and is a Concept factory rep.

http://media.crossfit.com/cf-video/CrossFitC2_1BasicOnRower.mov

I rowed 2000m last week and attempted to hold a 500m/2min pace. I held it for 1000m/4min and finished the row at 8:12

World class crossfitters like Jason Khalipa can row sub 2-min 500's sustained. He held a 1:50/500m pace for the half-marathon row at the 2013 Games.

Last edited by Take_a_knee; 04/08/14. Reason: added info