I believe the max poly count for any single EA item, hair, clothing etc. so far is around 9K and that is one of the hair pieces (The Island Living one I think) so I consider anything above that number as "High Poly". I've done so many tests on this since I have a 2012 MacBook Pro lol
IMO most of the lag and crashes come from Edge Smoothing (Anti-Alias) & Lighting being too high since they're the most demanding aspects of the game. When you add CC you have to take in account of those two settings. I use to play with Edge Smoothing/Lighting on High but after I added GBs of CC over time I had to reduce the settings because I started getting crashes & more lag. I was able to play on max settings with 1GB of CC, now I have 4GBs and the Sims setting is the only setting I can play on Very High without major FPS drops or crashes