How reliable do you want to be at a given level of performance?.
36s, and 40s mean just running static. If you like that, and the shortcomings that go with that, fine.
But, if your one of the lucky few that has headgaskets problems, with doing that, then going to the 50s will cure that.
And if you get serious about going fast, you'll need 50s anyway.
The problem with static injectors at WOT, is that as they transistion from normal operation to static, they can be erratic. That's just fact, and often overlooked. The more ocassions that you run erratic, the greater the chance for blowing a headgasket.