heres some of my post pro work, these are my first attempts at post pro. crits welcome and needed 
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I don’t know what postpro you applied to the car but I don’t like it much…
the plane came out very nice though. I’m curious for theplane picture: how much was rendered and how much postpro?
The sketch filters are a bitover used on the car image. You can clearly tell you applied them, which is what you typically want to try and avoid. Play with the different layer settings, (i.e. opacity, fill, type of layer, etc.), to get the final result that will not clearly show the filters used.
You can get a hand drawn look from a clean render without the roughness that you have.
The plane is very well done, I agree with Gr8RedShark there.
BgDM