There are a number of issues you need to consider. First, where are the data coming from - all of these data use some sort of interpolation and you can't make data where none exist. So, even 1km is too fine for many areas (and the developer of the technique commonly used for this interpolation recommends not going beyond 5km). There is also a link between spatial and temporal scales that becomes very real at smaller scales (does the temporal resolution of the climate data match the spatial resolution desired). So, it would be good to find out more about what you are trying to do. People have downscaled to 500m for parts of Europe but that does not necessarily make it correct.