I'm just trying to decide whether to leave this archive uncompressed, people seem to think it's a good idea as it saves CPU time. But on the other hand it's having to pull twice the data from the SSD, has anyone properly tested this?

It has been tested. Your computer will access compressed files faster than uncompressed ones.

There is a thread, I don't have it marked. I wouldn't say consensus was reached, but everyone who actually knew enough about computers to have a say agreed on compression. There was also much reporting of what could be placebo effect.

In my own experience, moving the game to an SSD had a dramatic effect on loading times but nothing else.

Cheers!