Really?!! ;-)
Inevitably more noise comes from the 4.7 and no roof = Cabrio. From dipping my toe in this market - or rather having thrown my bank account into it just now - Tilum's earlier post here...
http://www.sportsmaserati.com/showthread.php/15157-Gran-Cabrio-variants
...gives a good overview. But, the key points (lifted from the aforementioned) are:
1. GranCabrio
2. GranCabrio Sport (pre-facelift, similar to the GranTurismo S)
3. GranCabrio Sport (post-facelift, similar to the GranTurismo Sport)
4. GranCabrio MC
N.B. All have a 4.7 litre engine, and all have a 6 speed Auto gearbox (i.e. with the gear lever). However the Sport and MC models have a more powerful version of the 4.7 litre engine, better brakes, and have the very impressive MC Auto Shift software (allowing 'proper' manual control over the gear shifts), and the Sports exhaust (as per the GranTurismo S, and Sport models).
The GranCabrio MC is different again. It's the convertible version of the MC Stradale, and it has the same bonnet as the original (2 seater) MC Stradale (which has 2 air vents), brake cooling vents on the front side panels (as on the MC Stradale), and the MC Stradale exhaust (two single circular sports exhausts mounted high up above a rear diffuser).