I recommend tenacity on Custom Hydra and Heavy Splatling Deco, not always, but very useful. For Mini and Custom Hydra, I use up to the equivalent of 5 mains of run speed. On all splatlings I use at least 3 mains of run speed.
Main builds:
Heavy Deco:
4 mains run, 2 mains swim
Tenacity, 4 mains run, 1 main swim
Zimi:
5 mains run, ink resist
Custom Hydra:
5 mains run, tenacity
5 mains defense, bomb sniffer