The world I've been playing forever has a lot of 1.6.4 terrain generation and is currently in 1.7.10. One key and critical difference I've noted just recently in the terrain is when I've searched for clay, in 1.7.10 its gone from the oceans, making it obnoxiously more rare and difficult to obtain than it already was.
Is there a map mod or program that can lay out your map and recognize which sections of terrain were loaded in which version? This would be incredibly useful for innumerable reasons, certainly for me mapping out how much 1.6.4 ocean terrain I have left to scour.
The closest that you can get is to use a utility like AMIDST, set to use 1.6.4, and compare what it shows to what Minutor (which shows the actual world) shows since the game doesn't save what version a chunk was generated in; you should also be able to see chunk walls between pre-1.6.4 and post-1.6.4 terrain, as well as take advantage of the fact that oceans are deeper in 1.7 (you can set the slider in Minutor to around y=45, close to the maximum depth of 1.6.4 oceans, while 1.7+ oceans are about twice as deep; normal ocean still does generate in 1.7+ but it is more of an "edge" biome with most of the oceans being deep ocean):
Yeah I've seen the terrain borders in my world, should be easy to recognize on a map. Also if I remember minutor shows the material of whatever y axis you're examining, the entire ocean floor of 1.7 is just gravel... sure it looks nice but holy crap what a stupid decision. I miss 1.6.4 ocean biomes in general, they were unbelievably huge, which was realistic. You could hide structures in them no one could ever find.