(Slightly) Better than composite but not as good as rgb. I found this manual here: http://www.go-gddq.com/upload/2009_0...2412217802.pdf which is not your model but might be the same chassis. It matches what you say about the black and blue scarts sockets. They are both RGB enabled.
RE: Svideo/SVHS Ok, I stand corrected. Thanks
One way you can tell for sure if you are using RGB is to go into the ps2 config and deselect RGB output. If you are connected via RGB then everything will go green when you select Ypbpr. If you are on composite then there will be no change.

