Maybe a current student can clarify. Actually I would really wanna know. I'm from Orange County and UCI was my top choice.
Copy/pasting from a post from last year:
"Irvine is P/F for preclinical years, but it has a hidden ranking system (i.e., they keep track of your performance, use that to rank you by the end of the fourth year). That rank is reported when the Dean or whoever writes your letter of recommendation for your residency applications, not as a "2/100" but more like "performed at the top of his class", "performed in the top half of his class," or... "performed in a satisfactory manner."