If your dubt is 3.0i versus 3.0sd, I strongly suggest the second one, in particular if you like to enjoy accelaration and impressive torque..

As for my experience, petrol benefit are: better sound and better "driving fluency". Disatvantage: high consumption compared to diesel.

Diesel disatvantage (but only extreme limit example, you have to be really unlucky to run into): the engine is more "delicate" (in particular if high powered, like in our case) so you have to take care a little more on service; risk of engine damage in case of fuel contamination (like water or other impurities, could happen with diesel); easy generation of impurity in the bottom of the tank (I never suggest to exploit the reserve with a diesel!); cold sensitive (in case of very low temperature it can freeze, an additive or a special winter type is necessary).

I suggest to purchase the 4.8i, if not possible, wait for the 3.0sd, but in case in the mean time the 3.5i 300hp will be available this is the perfect comprimise.

For your info actually I'm waiting for the 3.0i delivery, but given that it's postponed because of an option (Tobacco leather), probably I take the opportunity to switch the order to 3.0sd.