Maximum effective distance of ethernet?

I dont think there is one

The maximum distance for 100Base-TX (standard ethernet cable) is 100 meters. This would be the distance from a switch to a PC, The maximum total distance between 2 devices connected to the same switch would be 200 meters.

I believe you could cascade switches together to further increase the distance, but I am unsure of the details.

If you went further than the 100 meters it is likely that you would begin to have an excessive amount of packet collisions, reducing your effective throughput.

100base-T is officially limited to 100 meters, but I have pushed it out about 120 meters before with no problems.

I have also pushed 10Base-T out past 250 meters to link two buildings and it has been stable for 9 years! Of course I used the best Belden CAT5 I could buy at the time...