I dont think even 5" speakers fit into 1k doors eaisly. The windows come down a fair way and block all the existing holes in the doors. Else you have to cut some steel away from the door to fit the speakers. You could also use risers but the doors in the 1k are close to the driver/passengers, so risers would poke you in the legs.
I was going to use 4" splits in my 1k at one stage. They may be small, but its a small car, and huge speakers are not needed.