I pretty much do what MM does and just buy one fuel, in my case I use Power Master 15%. It is the number one fuel in my area, comes up on sale A lot so it's around 15 bucks A gallon and I stock pile it when I have the money. In Calif. we had club members buying pallets of the stuff and we would get A great deal on cases. Nitro content is mostly to to help with the idle of the engine and you will get A power boost as more is used. No reason to say any more about it, the hows and whys of it all. If you want you can do A search on nitro and read for weeks what everyone has to say about it. If you go to Europe and fly it's either going to be hard to find any nitro fuel or cost way too much. FAI fuel is just the alcohol and Castor blended and used as fuel in most countrys besides the US. If you want to use 5% it isn't hard to tune for it and it works quite well for sport flying. If you can, borrow A tank of different percents from club members and see what happens, you will find A surprise or two.