Nice to know.
Intuitively thinking now. All caches no matter how large will eventually get full if you don't clear them. (Like Newton's 4th Law or something.) Once full, the browser needs to find something to evict from the cache to make room for a new file. That's gotta slow things down some.
Are you expanding the cache size to delay the inevitable?
And if the cache is 50% bigger would that mean it would now take N % msec longer to fetch it? Is there a point of diminishing returns where a bigger cache slows the browser down?
Anyway, I run my FF cache at the old max, 1024 MB like you were. I noticed today the game slowed down, putts stuttered, pauses in the backswing, etc., I checked and my cache had 900+ MB used. So I cleared it. The next game ran better, loaded OK too. And I had a 25mbps download pipe.
Again intuitively, adding 50% more paper to my desk wouldn't seem to allow me to work faster. Hmmmm.