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To get the max speed (without Brightwater testing) increase it to 1000% with Laquine Ear, you'll need to save scum to only get the transformation you want and don't forget to remove the ears in appearance menu to avoid full transformation, then get the synthetic womb.
The egg slit testing being a multiplier should be done last but since it's quest dependant not sure if you want it.
Edit: The breed hungry perk also increase incubation speed it's a flat bonus to the incubation speed affected by transformation and synthwomb.