I bought extended range tanks, and haven't used them yet. Now with the even larger standard tanks, the range is about 6 1/2 hours flight planning at 8ph.
I would divert the cash elsewhere if I had to do it again.
The standard 52 gallon tanks gives you 5.5hrs of endurance before you dip into the reserves. Adding on 12 gallons means you would be airborne for 7hrs before you get into the reserves. Unless you were looking to fly distances where you were incapable of landing for 1,000nm I'd say at this stage it wouldn't be worth it.
I don't think it would change much of the flight characteristics except for the fact you'd have more fuel than passengers/luggage, but if you were in the air for 7 hrs I would hope you wouldn't have to worry about 3 other bladders. It would add maintenance as you have extra valves and maybe pumps.
The only place you truly would need a ferry bag or that kind of extra range is if you were flying from the mainland to Hawaii. The hops from Canada across the North Atlantic is done in 600 mile legs, so I'm not sure you'd need the extra fuel tank for even that one. If you're going down the Caribbean way you'd just go through the Bahamas and skip down the islands from there and you'd be well within range of the 800nm on a standard tank.
As for the G3X - I'd imagine it would incorporate all that like a champ.
I have the 20 gallon extended range tanks along with the original 46 gallon main tank capacity. We’ve used them a number of times on longer trips as a way to carry more Mogas and use less AvGas. So if we fly from the San Francisco Bay Area to Tucson, AZ, we can carry bags and buy MoGas in Tucson for the return trip or just buy the minimum AvGas necessary.
If I was building now, I would use the new 52.2 gallon tanks and not add the extended range tanks.
