My first thought was to ask what size plane are you already flying and where do you want to go. If you've already got a .40 size plane then staying in that size range lets you reuse engines, props, etc. This will save some money. However, if you want to move up to a larger size then .60 is certainly an option. For the engine choice, you could save some money if you went with the K&B .61 Twister instead of the OS. It's got similar power and weight, but quite a bit less money. It's model number 6170 on this page: http://www.mecoa.com/kb/aero/aircraft.htm