I figure I can probably keep two or three problems in my head at once before I start making mistakes, and my branches stay in my head until they're merged or abandoned. 40? It'd be impossible. Maybe I just have a weird brain though (or am just not a good engineer, based on what I've read about stacks elsewhere since reading this post.)
You wouldn't do 40 completely unrelated things, they would be 40 aspects of a single thing. I would think 40 is getting a bit big as I have trouble getting stacks of more then 15 past a reasonable review, but the good news is ( at least with some tooling ) you can commit partial stacks, so I can let my team review the first 10, while I am working on 20-30 and everything still just works ( even after I merge the first 10 into the main branch )
The stack of 40 is usually quite related and often would be a 2-3 PRs in GitHub -- it also lets you perform pipelining where you can add new commits to the end of the stack at the same time as merging commits earlier in the stack.
