I haven't ever smoked anything that scared me off from being too potent. On the other hand I have on multiple occasions over did it with sativa edibles. Now that doesn't agree with me at all and high doses really suck for me. I ate several cookies that each had about .25 grams of concentrate (decarbed in butter), I think it was 5 or 6 cookies, definitely 1000+ mg. The anxiety levels max out, room starts spinning, tile floor looks like an ocean of waves moving. and it lasts for hours like that. Sleep is nearly impossible for me until that phase of the buzz starts to ease up.
Now back in the mid 90's I popped a bean that a buddy gave me. It grew into a short indica that made beautiful large calyxes that were thickly coated in trichomes that looked like salt they were so large/coarse. Pistils were fat and bright orange, not tan or rust. As plants go it was a runt because it had sprouted last out of that batch I cracked. The leaves were very indica, round football leaflets that overlapped with very rounded serrations. It was the first plant in that batch seeds to be ready for chop. I didn't get more than an ounce off it but that was mostly in one large top.
I had set it aside to dry and forgot about it for a week or two as I had plenty of various different plants to smoke. I remembered I had it one day after waking up from a good nights sleep. I was ready to wake n bake and get on my computer to do some gaming (man games were primitive back then lol). I packed one nice full one hitter on the bong and ripped it back. Talk about sledge hammer indica. Instantly completely stoned, couch lock to the max. I smoked a cigarette and went back to bed. It made me so sleepy. Good thing it was a Saturday. So after a good 4 hour 'nap' I woke up and repeated the process, figuring no way the weed could really knock me out again. Well it was beddy bye bye time again. I slept another good 3 hours or so.
After that experience I only smoked that nug right before bed and the one friend I gave some to was told he had to go home to smoke it. It knocked him out too. Unfortunately that plant was pretty small when I flipped the timing to flower so I didn't take a clone as that would have been half the plant and I was unable to reveg it to keep it around. Still to this day, a good 25 or 26 years later, that is the strongest indica I have ever smoked. I would have loved to play with it more to see if chopping it a little earlier would have lightened up the sleepy part.