Okay did some of my on testing and this is not a certified test but just what I found on my layout with my equipment. This was all tested using Conventional mode only with handles on both transformers.
Lionel 0 gauge tubular track and layout is 13.5 feet by 22 feet Double main line. Flat board no inclines.
22 toggle switched blocks. 2 toggle switches for changing from Conventional to Legacy/TMCC
Fluke Digital Meter
Pure sine wave Z4000 MTH Transformer
Starting volts against a E7 AB Williams with True Blast II pulling 6 MTH Passenger cars.
AT 9.5volt no horn or bell at this voltage
At 10 volts got horn and bell but running at a good speed.
At 11 volts running at a good clip.
At 8.5 volts running at a correct speed but no horn or bell
At 7.9 volts engine stops
Now same setup with Lionel Modern ZW-C with two 180 bricks one for each handle.
At 7 volts light on and engine can blow horn and bell engine not moving
At 7.5 volts engine crawls and moves
At 9 volts engine running at correct speed
At 10 volts engine is high balling speed
Setup now is a Lionel SD60/TMCC with 9 freight cars.
MTH Z4000
At 7 volts nothing
At 8 volts some chatter in the engine
At 8.5 volts lights on dim and a clicking sound from engine still not moving
At 9 volts engine moves at a crawl but no sound or bell, smoke
At 10 volts engine running a correct speed with sound and bell with no smoke
At 11 volts engine running at a very fast speed but sound and bell and some sign of a little smoke.
At 12 volts engine running way to fast but smoke is working and sound.
Now same setup except Lionel Modern ZW-C with 180 bricks
AT 6.5 volts sound is on and bell no smoke engine now moving
At 7 volts engine starts to crawl with sound but no smoke
AT 8 volts engine a correct speed and sound and smoke working
At 9 volts engine high balling and sound and smoke working nicely
At 10 volts engine running to fast but all is working good
It seems to me for what I have tested for now the ZW-C wins the way for operations for me now. Seems the chopped sine wave makes the Lionel engines run much better than the pure sine. The Williams engine work much better at a crawl speed but did notice that the electronic E unit did not like the function to go into neutral with the handles and I had to use the direction button to get it to reverse but, not every time and that could have been the voltage at which I was at when I tried it. The direction button to me is not a deal breaker.
This is just what I found on my layout setup. Maybe this can help some understand the differences.
