What number would actually stop you from breaking ground

Working through what a first ground-up costs and I've noticed everyone has a different tripwire. Some people say untrended yield on cost, some say the spread over where they think exit cap rates will be, some say they just need to be able to cover debt service at 90 percent occupancy.

I've built a spreadsheet that says my little 8 unit idea works at a 6.4 percent untrended yield on cost against a 5.5 exit cap. That's a 90 basis point spread. Someone at a local meetup told me nobody with sense builds under 150 basis points of spread anymore, and someone else said untrended yield on cost is the wrong test entirely because it ignores that rents in year three won't be today's rents.

I can see both. Trending rents is how people talk themselves into deals, and refusing to trend them at all means you never build anything in a soft rent quarter, which is apparently exactly when you should be starting. So the underwriting test you use is doing a lot of quiet work in deciding whether you ever break ground at all.

What's your actual go/no-go number, and is it a spread, a yield, or a coverage test?