R.O.

I usually go for Y on short- and medium-haul flights.

For long-hauls, I do have a preference for premium cabin. But I still will do Y on occasion. Depends on whether it's a day flight or a night flight. Also depends on the price differential of Y vis-a-vis J. Another factor is whether I have elite status with an airline (if I receive free exit row seats or free eco+ as an elite, the premium I'm willing to pay for C goes down).

So there's really not one limit. My tolerance of Y is contingent on other factors.