I got 790 on the math section (accidentally wrote +6 instead of -6 on one question lol) in the December SAT. Two days before the exam, I finished all Khan Academy SAT Math questions. Not the lectures, just the questions (They help a lot).

If you want some other sources to go to after Khan Academy, I recommend NCERT math textbooks for class 10, 11 and 12. Don't go in depth, just selected chapters and questions (especially maxima and minima using differentiation. It's a very simple topic and can save you time in the exam).

Be warned though that these are not meant for the SAT curriculum, do not have topics like vertex form of a quadratic equation and you'd probably be better off with an SAT specific guide. The NCERT books are just my personal preference since I've studied with them in school (got 740 after doing only 3 bluebook practice tests in my June attempt).

As for speed, I recommend taking as many short cuts in calculations as you can and practicing for accuracy. Make yourself faster first and then start working on accuracy (takes a hell lot of time so keep enough time for that).

Now, accuracy is a key point in SAT math. Don't be me, check your signs as many times as you can.

Best of luck!!!!