The Cobra option is the better one to go for if you ever plan on changing the backbox, it will require cutting and welding a flange on with the reveloution as it is a slip jointed system, both are quite and should be sub 100db static, (not 110 that is far too loud!) Both are also free flowing and true 3" systems.
The other option would be a Miltek system but you need to budget a few extra ££ for that.
I pass sound test at all track days with ease with the Cobra trackday system on, (and that is with a custom 4.5" exit on the backbox) you can specify the finish you would like when ordering. When I'm feeling noisey I fit a 3" slash exit Hayward and Scott backbox
Most other exhaust systems are too noisy or not true 3" (they have some width reduction somewhere in the pipe work, Usually at the downpipe to system flange/fitting) and fit isn't so good.
hope that helps,
PS avoid cheapy cheap stuff!