Backpreassure is worth thinking about. (not the diameter of the compressor) All standard chips for different stages covers a wide range of modifications. The only two things you got to have exactly right is the MAP-sensor and the injectors. (of course a stock and a max flowed head with uprated manifolds and cams need different programs) The point is that all the small parameters (like going for a little bit bigger turbine) can be adjusted for by adjusting the fuelpreassure. If your engine is running ok but you fit a bigger turbo and maybe a bigger exhaust, you should increas your fuelpreassure just a bit to be sure. An air/fuel meter does not cost much , and will tell you if you're running lean. Mine is working just fine...