I'm also curious to see how stressed you were working at a start-up. If you're getting as much stress as the founders without the potential upside, it seems like in many cases it may not be worth it.
Stress is something that comes with doing exciting, scary things. Sure, having a comfortable day job and working on a side project on the side might be fun, but it's probably not scary and big, unless of course the side project becomes something big. At which point you'll be stressed again.
At 75-100k you're not losing that much happiness and stress wise if you take a pay cut at a start-up.
If you have an offer of 40k at an established company and are taking a lower salary (30-35k) to work at a start-up, that will hurt significantly in terms of your happiness, stress, and your ability to pay your bills.
http://dalethoughts.com/2012/03/entry-level-start-up-job-or-...
The combination of working at a big company while having a side project may outweigh the benefits of working at a start-up (at an entry-level gig).
At the entry level, the pay-cut you're taking by working at a start-up can be significant on a personal level. For someone who recently graduated college choosing between a 40k gig at a big company and a 35k gig at a start-up, that 5k will be much more significant than an engineer taking a pay cut from 85k - 65k.