I installed the same size using the original door panel. Drilled new holes in the door and then trimmed off the inside of the plastic panel around the original speaker cover with dikes to make room. It's a tight squeeze, but it all went back together and appears factory!
Now that you mention it, you are correct. It's been a while back, but I believe I had to remove and reuse the factory speaker spacers, which in turn is why I had to trim the door panels.
Evening Patrick. Best I can remember they were 5 1/4" factory. You'll still probably need to reuse the spacers from the original speakers to clear the window track.