40 liter tank
I bought a tank from Stuart, you only need to fill it up on parts of the trip where extra fuel is needed to be carried. Run with 20 litres as per normal.
I have replaced the standard fork springs with progressive springs, much stiffer to cope with the extra weight.
The reason i went for this set up is on the West African trip i did, mounting 2 x 10 litre jerricans on the bike was troublesome and expensive. This option means no messing around with jerricans and extra mountings and the extra capacity is always there if required.
My 2 pence worth