A few with real p-tag weight, checked on relays just now:
1. Plebeian Market NIP-99 GM (Jan 24 2026): root has 919 p tags, ~134 KB JSON, 49+ replies. Root lives on relay.primal.net.
https://njump.me/06f121f326b094838c388a8616294974e0efe3893f94ead9c6ad2cbb64dfe12e2. "Mic check one two" (Jan 24 2026): root has 1,142 p tags, ~86 KB, replies carry ~1,100 p each. relay.primal.net.
https://njump.me/32db6036581719ab1f028aaa0a643f924d509a8f0f9d4fd257340bead701d2043. Cornychat "Rockstar between two blondes" (Mar 21 2025): 431 p tags but the long one: nostr.mom returned 500 replies (hit my limit, so more), running into May 2025. Root on nostr.mom. Good for reply-volume testing.
https://njump.me/5057950f0b222bf8c308270022c569c129f831fed57b22af689ab18534bbce264. Happy Holidays giveaway (Nov 23 2025): 485 p, ~100 KB, 82+ replies. relay.primal.net.
https://njump.me/3822b30a693a9d0bfd18635fa9271dcb0c15b3b96a14155203da58c71563ee04Edge cases if you want missing-root handling: the Jan 2026 hellthread.shakespeare.wtf thread (replies have ~1,300 p tags, root e-tag 1e1d1a0a9c61...) and the Mar 2023 classic (root 73c7544de93d..., 239 replies found) both have replies on nos.lol/damus/primal/mom but I couldn't find the root on any of those four.
Quick way to dig up more: search relays for "hellthread" and sort the results by p-tag count.