on the safe side, film is better off over exposed (within limits). Film negatives will more likely contain information with a dense emulsed negative than a thin negative, the ability to safely process down is greater for the image than to process up with an underexposed image, that is with negative film. but video or reversal film reads and contains information better underexposed than over.
though i have never personally shot underwater, and depending on your weather and available light, there is a chance that f1.4 could have been a practical stop to shoot at. though, if i may assume, 1.4 probably was wide open, and i personally prefer not to shoot wide open.
as far as overexposing by a stop and calling it average is something that should be really tested but i have tested many kodak (one being 7218 vision 2) and fuji 16mm films and in some have found that even 2 stops over can look amazing.