The 1957 is one of the more common silver Washington quarters in Gem condition. There are a large number of Superb MS66s known.
Although this date is among the easiest in the series to locate in MS66 and even MS67 grade, when it comes to upper end MS67 quality, the coin becomes fairly scarce as is the case with nearly every silver quarter in this series. Interestingly, at the time of this writing (and PCGS has been open for business for more than (25) years now), not a single MS68 (or even MS67+) has been graded of this date. I would personally expect to see a few MS67+ coins graded at some point in the near future, but good luck in the hunt for an MS68 example! Also, of note ... virtually every coin that has achieved the MS67 grade level is a mint set toned or album toned specimen. Blazing superb gems from original rolls (without toning that can often hide imperfections) generally max out at MS66 grade. In my near (25) years of hunting for this date in superb gem brilliant PCGS-MS67 grade, at most I recall seeing just a single example. Finally, be on the lookout for the "Type B reverse" of this date as finding one already in a MS67 graded PCGS holder would be a good "cherrypick"!