I cannot seem to find that file, though I confess I did not look TOO hard. The game is silky smooth again!
I lowered the graphics, closed the game, did nothing. Lowered them more, closed, nothing. All the way to the bottom, close, and... it worked! And then I incrementally raised the graphics back up with no further issues!
Clearly I am no computer genius.
Thanks for your reply, though, it really is appreciated! I feel kind of bad you even wasted your time writing that.