Thanks everyone :-)
Had a load of trouble trying to find a tyre outlet that were in anyway helpful. Tried 5 tyre shops in the vicinity of my work, all of them among the larger retail chains, not one of them had 295/45R20's in stock. 2 of them even tried to tell me that the Pirelli's were the ONLY make of tyre that would fit my car. That 5h1t may have worked before the invention of the Internet, but in this day and age when anyone with basic computer skills can do 5 minutes of searching and find any number of options it really does them no favors. They immediately make themselves look either incompetent or deceitful, either way I'd never deal with them or recommend them to others.
Ended up finding a small, locally owned and brand unaffiliated shop that were able to get me 4 x 295/45R20's in for fitting on Friday. I was going to go for a set of the Toyo Proxes S/T II 114V tyres, however they couldn't source a full set. Ended up going with a set of Nankang SP-7 114H as that was the only complete set they could source overnight. Perhaps not the best available, but they seem to get ok reviews
and are noticeably smoother on the bumps than the Pirelli's.
Did about 200kms yesterday up through the Macedon Ranges just north of Melbourne. Managed to achieve an 11.5l\100km average with very tame driving and Eco mode off. Pretty impressive considering they are windy and very undulating roads through there. That is very comparable to the 2011 Toyota Rav SX6 that we had before the Jeep.