It is about the board score, and clinical grades more than it is about preclinical. But this is a kind of misleading way to look at things in my opinion. If your best effort is average then i think its more likely than not that your best effort will be average on the usmle also..
can you work harder than you did? do you want to in order to guage your true best effort? Then you know what to do. Your best effort for the rest of pre-clinicals will probably translate into a better board score than you would have otherwise anyway.
tempted to link the "inches" speech. life is a game of inches. fight for every inch cause when you add them all up, it makes the difference between winning and losing.
edit:
http://www.youtube.com/watch?v=f4XTxWNRg0Y it's about football and its pretty dramatic but its a pretty cool scene