Maybe 'drone' was the wrong word to use. On my test drive I found the constant noise (from the rear of the car) quite annoying and am pretty sure it was the exhaust. I'm not used to 'performance exhausts' in any way so it may be something that you guys are used to and don't notice or that you notice tyre noise more?
I'm not complaining that a performance car sounds like one - I just thought that, in say Comfort or ECO mode, it would have been a bit quieter.
About half my annual mileage is on A roads/motorways but there are a few weeks in between these trips. If I was on the m/way every week then I'd definitely consider a GTD but I think my driving pattern probably doesn't suit a DPF.
And want to add many thanks for all the helpful advice on this - even taking test drives to provide feedback. I've not got much experience of other forums but doubt there is one as helpful and informative as this one.