Even if it is just marginal.. I'll take it.
And that's why the choice between 9mm and .40 usually just comes down to personal preference. With, say, a Glock 19 I like how I can accurately place my shots faster than I can with a Glock 23. That, and I have two extra rounds in the magazine "just in case". You, on the other hand, like having a round that is slightly more effective per shot. There's nothing wrong with either approach.