Please find a dictionary and look up perspective. Then try prospective.
To answer your question, I need to know more information.
What is your cumulative SAT score?
Did you take the ACT? What was your score if you did?
Do you anticipate getting scores higher than 680 on your two upcoming SAT II tests?
680 is a great score. It's by no means perfect, but if I were you, I would send it in a heartbeat. However, I'm a fairly poor test taker. If your other scores (both on the SAT and your upcoming subject tests) are immaculate and all above 700, a 680 might ruin the wow-factor of having all 700+ scores. However, if you have at least one of the 3 components of the original SAT below 700, I would send it.
To simplify: If CR=700+, M=700+, W=700+, and both other SAT II= 700+, don't send the 680.
If CR, M, W, and/or either of the two upcoming subject tests are below 700, or if you have any scores in the 500/600, send the 680 subject test.