What does tuning PostGRES do?

[WhiteRider]

It is likely that the full 6GB isn't available, or the 6GB profile would have been used (even if you have somewhat under 6GB available I'm told that would still be used). In that case the settings are probably pretty good for you. You may be able to get further slight improvements by tweaking the settings manually, testing, re-tweaking, testing ..., but I doubt it would be significant, and going too far with the settings could make things worse again. The values that we set should be a significant improvement over the defaults, which are far from optimal for modern systems.
(Note: I don't know as much about what's going on behind the scenes here as Kraada so he may be able to advise you more accurately.)