S905X2 4G fast or slow?

How can you tell if you should use the fast or slow 4G version of s905x2?

And what are the signs that you’re using the wrong one?

Ex.
I have a T905Q and ps1 plays well with most games, some pauses but n64 is unplayable for most games.

Any help is appreciated, my first build. Having a lot of fun.