Retake SAT again and/or take the ACT?

I just got my 2nd SAT score back- a 2040 (680 all). First time was a 1870. I am a rising senior.
I am wondering if I should retake in Oct. I am probably going to UWashington (resident), but I want to apply EA to Stanford (where my score would be less than excellent…)
Or, should I try the ACT in September? I have never taken it.
Also, a Stanford alumni told me that Stanford doesn’t exactly want someone to take the SAT 3 times.
I am also taking 2-3 SAT subject tests.
Other colleges I am applying to are schools like the UCs and Cornell.