That said, unless you have a really stiff back, you should try to position yourself as low as possible, and keep your width as narrow as possible. If you are younger, and you have a comfortable fit, but one that puts you nearly upright with a very wide stance, you may want to think about SLOWLY changing that to a more aero fit. But I would only recommend doing so if your position is significantly out of whack. If you sit up and look out over everyone's back even though you are only 5'5, or if you need a small car's width to pass, you may want to explore your options a bit.
For all the talk about flat backs - and from an esthetics point of view, they sure look fabulous- there are quite a few world class time trialists that don't even come close to being flat. It also bears keeping in mind that the flatter you want to be, the more you will need to rotate your hips, and the more likely you are to sit upon, and do damage to, some very sensitive and important parts of your anatomy.
Although this isn't discussed openly, saddle comfort is a key determinant in long term cycling success. I personally know of professional riders who had to cut short their career because of recurring saddle sores, numbness, and what the medical profession calls, genito-urinary problems. Usually such problems can easily be avoided by a shorter top tube and a somewhat more upright position.
A new position is usually the only option, notwithstanding the current crop of saddle shape modifications. These ingenious contraptions often do nothing more than shift the problem, or in some cases, create new problems where none existed before. Cutouts may reduce pressure in some locations, but because of less material they are likely to increase pressures much more in other spots. Gels heat up after a hour or so in the saddle and thusly promote inflammation. As a rule, the solution for a saddle problem lies not in the saddle but in the overall position of the rider.
Today, 3,000 meter swim (160 laps). Weather is nice but on the cool side.