From the FAQ, I'm not sure I understand ReserveCache, but I have it set for 45 (without that, ttsd, emphatic and empire all at once was too much).

It looks like it tells the player to use less RAM for caching, is that about it?

Yeah, it's the torture test. I like to push stuff to the limits. With ttsd, I started with a couple words, then went for Hamlet's soliloquy... it chose "not to be".