i concur with akittka that percentiles are not more important. Though i have no factual evidence to back this claim up, i do have my logic.
Notice that the percentiles for 800's on various tests are not all the same
http://www.collegeboard.com/prod_dow...ntileRanks.pdf
Let us assume that percentiles were in fact more important. In that case, 800 Ecological Biology would bear more weight than an 800 in Molecular Biology or one in Chemistry. Likewise, an 800 in Chemistry would bear more weight than an 800 in Physics. Does a student who scores an 800 in biology have a better shot at admission (lets assume they are majoring in something other than physics/biology) than a student with an 800 in physics? Absolutely not. In fact, most colleges say that they don't care WHICH science subject test you take, as long as you take one.
Perhaps an even better indicator of why percentiles don't mean as much as your scaled score is the fact that a 730 in math level 1 is 91st percentile while an 800 in math level 2 is only 90th percentile. Now you may argue that you can achieve either score by missing 5-6 problems, but tell me how you can conclude that the student who misses 6 "easy" math problems is as proficient as the student who misses 6 more difficult math problems.
The college board scales scores for a reason. keep that in mind