Prop selection is directly determined by flying style. If you want to go fast with it go for a 11x7 11x8 but if you want pulling power (aka unlimited virtical) go for a shalower pitch like an APC 12x4 or the ultimate .46 sized prop an APC 12.25x3.75 and it will be about as good as you can get for that engine. Definately bump up your Nitro to 15% as you will be pleasantly suprised. Still this does not garantee unlimited virtical especially at your elevation.