Agreed, your Up/Down SN margins are excellent -- you should experience no problems with values like these.
However,
the SN margin is frequency-dependent. The higher the Mbits/sec you
connect at, the lowet the SN margin will go. Currently, you say, you
are on Home 2000, so your SN margin is what you're getting for 2
Mbits/sec. If you move to a service which allows higher connection
speeds, the SN margin will drop (until some sort of balance is attained
between higher speed and higher fault rates).
This is where my
expertise stops. It would be good if someone, who knows how these
things tend to depend on each other (and it's not a clear-cut
relationship), would respond with an indication of what a Downstream SN
margin of 30.0 would correspond to at connection speeds of 3Mbits/sec,
4Mbits/sec, ... , 8Mbits/sec. Then you would get an indication of what
connection speeds you might expect if you "move up".
As a rule of
thumb, a Downstream SN margin of 12.0 shoujld be completely reliable,
10.0 probably reliable (though a bit vulnerable to spells of
interference), 8.0 is getting unstable (distinctly vulnerable), and 6.0
is likely to give frequent trouble (disconnections, re-syncs, ... ).
Hoping this helps!