I don't compete but I tune with the seat all the way back because it's the only way I can tune with the laptop...IN MY LAP and not laying on the console. I can adjust levels and time alignment for seating positions in the headunit with one channel pair of dash mids and tweets, pair for midbass in doors, and pair for sub. As far as l/r eq goes there's not enough of an audible difference to matter while driving and I have to have the seat up several clicks being so sawed off. Or maybe I'm just not as picky as some. I just know small level and time alignment adjustments are enough to compensate along with the eq in the Pioneer.
Also, one thing that took me forever to learn is that more times than not swapping out speakers will put you on an endless treadmill of wasted money. Fix the problem at hand in the install with what you have and then and only then decide if a speaker change is necessary. Some speaker locations in cars/trucks will fight you no matter what you put in there.
Speaking of speaker swaps I'm about to replace what I call the "perfect" 12" SQ sub with another great 12" SQ sub that only needs about 1/3 the box size. Hopefully I'm not making a mistake but will put the air pig back in if needed.