DB9 isnt a track car and whilst the V12 sounds awesome, you would be disappointed (relatively of course, it still would be awesome).
Audi R8 is a fantastic car. Very capable and took it to the Supercars establishment at Audis first attempt. The V8 version is great, but the V10 is superb.
The 360 is a Ferrari, and to drive any Ferrari on a track would be a dream come true for most car fans. Stunning sounding V8 engine, whilst the MR layout would give you a true supercar experience, possibly more than the slightly safer 4WD of the R8. Saying that, you would be much faster in the R8 as I presume you won't be a highly skilled driver, DONT TAKE THAT PERSONALLY, I mean you're not a racing driver? I'm being relative here. The 360 is apparently a handful for even the most capable driver at the limit, whilst the R8 is more forgiving. You could say the 360 would be better because of this, more fun getting sideways if they allow, however the R8 would be faster around the track in your hands, even the V8.
It depends how much you value Ferrari. For me that would be enough. Only you can answer that.
You will have a great day whatever! What track you doing it at Silverstone?