I made it to gen 7 in Sims 3 before the save became too unwieldy and unplayable.
I also made it to gen 7 in Sims 4 once with a family I loved and the whole theme was that they basically lived in a complete craphole (scrubby lawn, ugly house, etc etc). At that time there wasn't much in the actual game in the way of grungy items so I used a lot of cc to make the place look like a junkyard even though they were sim-millionaires at that point. I would add another eyesore to the property every time they hit a milestone; I think the last one I did was to put a pile of used tires on the lawn. It was hilarious (well, to me, anyway) and I loved that family but managed to accidentally delete the save when changing computers.
Those are as far as I've gotten in actual legacy play; all my other attempts from Sims 2 to Sims 4 have fizzled around gen 3. In fact I have a scored legacy and a random legacy sitting idle with Gen 3 kids. But in my rotation the first gen 5 babies are starting to be born.
