Its a matter of degree
If you are talking about mediocre - decent shoe games (Vegas strip rules, 75% pen), then you should be able to show a +EV with a lower spread. The question I would ask is not "what is the minimum spread to beat this game?". Rather, I would ask the following:
- What is the maximum spread that I can get away with on this game?
- What is the resulting SCORE?
- How does that compare to the other games I have available?
The answers to these questions let me decide whether it is worth my time to play BJ at all, and if so, which game I should play. I can get the answers to the last two questions in about 30 seconds using any of a number of software products.