And my own stats should it interest you also.
It all depends on the stability of your line. Sometimes a higher SNR is necessary to keep the connection stable. Multiple disconnects can raise snr and/or a fault on your line.
If you have a router that allows you to change SNR values, i'd recommend tinkering around to see what the line is capable of. I can get away with 3db but i do get a few more errors so stick with the 6.
But to answer your question, its a different case for everyone. I'm on a reasonably long line and don't really have issues with 6db but according to an engineer my line is great. Would i call 9db "normal" i'm not sure about that.
I'm sure you know all that though being "experienced"