Average Fight Length

Since my last estimate of fight length seems to be off, I'd thought I'd try from a different tack. One of my L6 playtest parties does an average of 45 damage/round with at-will powers. 5 L7 monsters have 400 hp. Thus it takes 9 rounds to defeat them. Reducing this for encounter powers, action points, magic items, feats, and occasionally dailies could easily reduce this to 6 rounds.