Roomiest 4 seat Convertible?

[100 IAN]

Looking to replace the wife's Saab Convertible and with 2x nearly teenage boys want something with good rear space especially leg room.

£25-£30k budget, Initial thoughts are

BMW 3 - she likes the retractable hardtop
BMW 6 series - I like the 635D engine
Audi A4 - I drive an RS4 so don't really want a matching pair!
Audi A5 - mmmmmmmm?
Merc E Class - good looks
Merc CLK - dated compared to the E Class?

and the wildcard.................... Bentley Conti (don't think she'll go for it and i know the budget would need to be streeetttched, but hey worth a try)

Naturally looking forward to a bit of practical research and dynamic testing but anyone any real life experience of which of the above is most spacious?

[Hitch78]

E Class or A5 are newest and probably roomiest. I love the Merc.