G'day, congrats on the new machine, that's an awesome upgrade!
Most people do change from the stock basket and find a dramatic difference, but definitely a good idea doing what you're doing and playing around with the stock basket first and seeing how you find it. I have a Pesado/IMS basket and get awesome shots with it, and many state that it was a big difference changing.
As for the IMS showerscreen I am also curious and would love to hear of others experience whoever has them! (I know the screen is kept much cleaner than any standard screens, but I was wondering whether it has a more even water dispersion, and whether that equals a much more even extraction)