Someone in another thread posted about their experience with breakables & increasing lag. Aside from the minor hang here & there, I had no issues playing this weekend until I ran Age of Rage and got to the room with all the breakables. There are plenty of high-density encounters in this quest, but none of them were glitchy until I hit that room & some crates were broken during the initial combat.
Even after killing the mobs, just moving around the room to complete the 'Sate your anger' optional was painful. Long delays between my action and the crates/bookshelves actually breaking, being frozen in place, disconnect between the sound effects and on-screen actions, etc. I tried experimenting with how I was breaking things, swinging a weapon for some groups, using an AoE on others, but I couldn't tell a difference other than breaking groups seemed to be worse than breaking a single item. No other lag issues during the entire quest.
This experience may or may not be anecdotal, but it doesn't inspire me to run quests with a lot of breakables. If anyone has run something like Smash and Burn recently, I'd be curious to know if they saw anything similar.