The 4000 and the 1200 were the same for game playability both have the AGA graphics but the advantage to the 4000 was more space inside the case for expansion. Sadly any of the accelerators made for the 4000 are VERY pricy to buy used.
That is my point, the 4000 already has a 040 stock in most cases.
you only need to change it if you want to go faster and have 128MB ram/fast scsi etc.
the advantage of the 4000 was the ide was buffered,it has a better power supply,comes with 040(some were 030 models),and has zorro3.