Adventures in bike fitting

I had a bike fitting done a while back.  Spending a few hours with a specialist carefully dialing into the right angles for optimum power. I had aero bars mounted and positioned right.  And then I got home and the seat angle wasn't right.  You wouldn't think that there is a lot of difference if the front tire is just slightly lower than the back but there is.  (The difference between being on a trainer, even with the front tire on a block and rollers that are flat)  I spent a ridiculous amount of money on a seat so that it wouldn't hurt and I get home and it does.  Needless to say I was not all that pleased.  So I attempted to change it on my own.  I did.  Or so I thought.  I also went back and bought different aero bars because my wrists were experiencing excruciating pain.  I went from s-bend to ski - bends.  So much better.  I thought I'd placed the new bars in the same place.  They were ok for a while and then they didn't feel right.  I readjusted them.  And then I finally took a look at my seat.  I hadn't tightened it properly after adjusting the tilt.  It had slid all the way backwards.  No wonder my aero bars weren't right.  But when I moved my seat back to where it should be it felt horrible if I wasn't in aero and I was just on my handlebars (unfortunately I imagine I'll spend a lot of time in this position not being too comfortable in aero and on a real hilly course).  So, how bad is it if I change that seat placement a little?  Does that really mess up my power efficiency?  I'm talking about a half cm difference.  And now I have no clue if my aero bars are positioned anywhere where they should be because I really did move them a lot to get comfortable when my seat was in the wrong place.  I already went in a second time to buy a different seat from the first one I bought and had that fit to me.  I'm embarrassed to go back in again, especially since the bike fitter made me promise I wouldn't mess with the seat.  But I had to.  

I wan't my bike to fit right.  But how much should I follow "the numbers" and how much should I go with what I can ride for 4+ hours?  Not to mention the 8 hours I think Canada will take me.