So I tried something different for the book I've just finished writing--I wrote my synopsis after I'd outlined the book, but before I wrote anything. I just went back to that synopsis and reread it. There were a few errors, where in my writing I'd strayed from my original plan a bit, but by in large it was spot-on. It was succinct, included the key points, and wasn't muddied up with details. Best of all, it took me a fraction of the time to write, because I didn't have to sift through all the details in my head (because I didn't know the details yet). I will most definitely be writing my synopses first from now on!