A lot will come down to what the models are that you want to paint for example Barrie shows quite flat large areas with little detail where the coarser 250 will be OK but if you are sparying items with surface detail or trying to get paint into hard to reach areas then you can end up with excess paint on some parts and little on where you actually need it. The 200 allows you to use deliver less paint for these tricky areas and then just open up the needle a bit more to increase flow at the same time as moving the airbrush further away then you can blow in the surrounding larger areas.
Likewise on your airguns if just blowing them over with black then the 250 may be OK but once you start wanting to do camo patterns etc then the wider heavier spray pattern of the 250 may be an issue whereas the 200 will allow for more detail.
The actual patterns and paint flow of the 200, 150 and 100 brushes are all actually the same the only real difference is the 200 uses the trigger for air flow and knob at the back for paint flow but the dual action 150 and 100 have it all control by the trigger which can take a bit of getting used to. There is also the third option which falls someway between the two of "progressive dual action" where the air flows before the paint starts to flow all from one trigger movement.
Do avoid Badgers with the IL or Fine head/needle combination as these are really only suitable for the very fine pigments in inks and water colours, a HD head/needle will cope with enamels and primers without excessive thinning.
Like Jim I just use the compressors regulator to set the air pressure I want coming out of the tank.
Edited By JasonB on 11/08/2020 19:00:33