All the FAIB models come with 2 paintkits, one for fsx and one for fs9. What I do personally is start with the fsx version, and once finished, I resize the psd to 1024*1024 and transfer my textures to the fs9 paintkit, then check that everything is fine as some smaller details tend to get blurred in the shrinking process and have to be reworked a bit in order to look good. Then you have to take care of the alpha channel which is a bit different, and of course make a specific lightmap, which is not needed in fsx.