Very simple imperial Kath, do you take VI or calculation

"very simple" isn't very simple; it's vague

do you mean "otherwise naked"?

if so, calculation imo. You at least want her ability to do something.

Very simple imperial Kath, do you take VI or calculation

What else are you taking? In general I would tend towards Calculation and play Scum Kath if I wanted a PS 9 Firespray.

Bit of context then Kath mangler cannon Recon Specialist

If you are taking a mangler, calculation is redundant. VI kath is Ok. PS 7 is a solid digit in this meta. I prefer engine on my fire sprays, for kath with mangler Lone Wolf could have a lot of value, that extra shot at rolling a hit on no focus turns could really help keeping the stress going. Tactician work somewhat, too. Stress Kath needs a second half of a list more than specific gear IMO. I took her to a tourney with lone wolf mangler tactician EU. She was the star of the list. But even with LW I failed to drop an A wing in 3 rounds of fire so there is that problem of dealing with 3 evade dice and consistency when a squad does not have multiple efficient ships.

I don't find Calculation to be redundant with the Mangler Cannon at all on Kath. Calculation works out of the rear arc unlike the cannon. Even in the front arc, Calculation still adds value since your opponent needs to cancel a crit to take stress. With two crits to cancel it is more likely that you'll deal stress and damage with the same shot.

Very simple imperial Kath, do you take VI or calculation

I'd take Predator over either (and Engine on top of that, if I have the points).