There are a few more things to consider, which include the two items suggested by Barnacle Bill. First of all, sailing dead down wind is the slowest way to sail down wind. In So Ca that is the point of sail when most beer can racers break out the beer and sandwiches. In my case, that point of sail was when I go to work. On boats that I was on that were middle to back of the pack I broke the race legs into individual segments. It is one way to relieve the frustration that you're a long way from first, second or third. If we did well on a given leg it was a win and a accomplishment.
We always did well on the downwind leg even though I hate that leg. Some races such as Newport to Ensenada, Redondo Beach to Long Beach and Long Beach to Dana Point were all down hill and while I never really looked forward to them we always did well mainly due to the fact we NEVER sailed DDW and even with a poor start we were able to easily pick off boats in front of us because we worked hard at it.
Taking tension off the backstay is only one part of the equation. To obtain maximum power, what little there is of it, you have to ease the halyard/cunningham and outhaul as indicated by Barnacle Bill plus a couple of more things. You want to use a "light" boom vang. By that I mean you want to use just enough vang to prevent the boom from rising. The Garhauer Rigid vang makes this proceedure a piece of cake. It isn't that easy with a soft vang and that is due to the poor pulling angle. Next you want the boom to be almost touching the shrouds. You want the top batten to be parallel to the boom. Also, don't forget the all important preventer. There is nothing worse than having the boom come flying back across the boat. It only takes a simple steering mistake by the boat driver for that to happen.
One other thing that mates forget is crew position. The idea is to keep the boat flat and by positioning your crew in the middle of the boat between the mast and the end of the cabin top helps you achieve that goal.