TU32/CU20/1.23/Patch 2, TU33/CU21/1.24/Patch 3, TU34/CU22/1.25/Patch 4
When I tried to recreate the lag in minecraft I found. If you have a lot of water in the world you get more lag.
So to amplify this I created a waterfall that goes on and off from Y200.
As the water is removed more and more lag is created. Meaning, I think, that the bugfix you made to remove the bug that created randomly water-sources is taking to long (much processing) to correct.
I hope this is easy enough for you to fix and recreate so that minecraft can be played in survival again.
I did not add a video since it is painful to watch.