The stock GP spitefire with stock OS 25FX and 9x6 prop will hit right at 100 mph straight and level. for a piped 25 FX the 8x7 will be a good prop and should be in the 17,000 range. The spit if properly built up will run right around 180 with a Nelson in it. Stock elevator is only good for around 130 or so and beyond that cant turn hard or it will shear off. Solid tail and then glasses with 1.5 ounce cloth works well