All, I know the GGAT2's are great in 18inch - have them on my D3; has anyone ever fitted them on a RR with 20's??
cheers

http://www.generaltire.com.au/tires/T5/Grabber-ATsup2-sup

305's are the wrong size for 20" rims. 2010 MY Vogue SE TDV8 3.6 Stornoway Grey- fully loaded

I know of people running 275/65 18's and there is one guy on RR.net who's running 285's - he claims no rubbing.

It all depends on what you want the bigger tires for - looks or actual off-road usage. The approx. equivalent in a 20" would be 275/55 20. If there are tires avail in that size and you are serious about driving the vehicle and not just cruising (or parking), that's about as big as you'll be able to run. Be aware that different tire brands have different sizing too. A 285 from one manufacturer may be a 275 from another 
RRC 2Dr, RRC 4Dr,
P38, and 2 L322s
(wife thinks I'm nuts - prob right, too)