They will definitely collapse as soon as the cache is filled. Especially with cheaper SSDs, fast caches are installed in order to be able to maintain the nominal performance data with small files. However, I can't tell you how much that will be, you might have to search for benchmarks on the internet or just try it and post the results here ;)

under Linux with random data via pipe on the file system (simulates an infinitely large file) constantly over 100 mb/s