Trying to get the "perfect" fit can be like trying to hit a moving target. As your body adapts to riding, you'll find that your position can change to accentuate the adaptations your body has made.
For example, when you first start riding, you tend to be a more upright. This is true until you develop some of the lower back, glutes, and hamstring muscles needed to support your body in a lower position. When you adjust your position so you are more hunched over, it amplifies your power by recruiting your glutes even more - and when they develop in response, you can drop your upperbody again. Of course this will level out and at some point you'll find yourself in the "optimum" range, with adjustments for gear (cold weather gear is thicker and sits you higher off the saddle), any physical issues (stiff back, etc), and any personal preferences (long hilly ride or super short/fast crit).
You also find yourself able to stretch out a bit more, again improving (usually) your aerodynamics.
From personal observations, I would say that one's ideal position is pretty set after about 3-4 years of consistent riding, i.e. relatively serious riding for 3 seasons for 3 or 4 years. This can be radically altered if there is an injury (Floyd Landis - hip issues dictated his position), radical experimentation (Steve Bauer comes to mind, with his chopper bike), or minor experimentation (Bernard Hinault fit a 1 cm longer stem to his bike in the middle of his career, Greg Lemond's seat was raised something like 5 cm after he turned pro).
The one thing that rarely varies is the seat to pedal distance (although changing pedals may drastically alter your seat height relative to the bottom bracket).
So, your current bike may be set up for you as of when you purchased the bike. But if you have changed at all since you got it (you ride more, you ride faster, or conversely you gained weight, you ride less), then it may not be ideal anymore.
Staying optimistic, a compact (or smaller) frame, depending on its design, will probably allow you to drop your bars more relative to your seat. This will probably make you more aero and improve power without changing your seat position. If the compact frame is also longer, it will stretch your upper body out a bit. If you are a fan of Jens Voigt's position (or Alexi Grewal for that matter), he has a very forward, very high seat, coupled with a faraway, low bar. Works for them, it might work for you. All position ideas have their advantages and disadvantages (high/forward seat, low/setback seat, long reach instead of having more drop, etc).
hope this helps
cdr
