Re: Some 166 queries!
I find the 6 speed gearbox a little stiff initially, but just until it has warmed up. Then, it's nice and smooth.
I don't think the 3 litre is especially loud, but mine has a Powerflow stainless steel exhuast fitted, so I can only speak from experience of this, rather than the original item.
Sat Nav can be retrofitted, but only economically if you have the wiring in place, apparently. As mentioned in one of the other posts above, there are threads elsewhere which cover this topic.