If you go with a lower rated cell it means you will have to have the cell/pump running more in order to generate the same ammount of chlorine than you would with a larger cell. That will translate into higher electricity costs. I'm in west central FL, have a cell rated for 40k in a 12k gallon pool and I run my pump generally 4h/day and have the cell set to 20% right now to maintain my ideal fc levels.
Don't forget you'll need to maintain a higher CYA level with the swcg than you would without so that you don't lose quite so much chlorine during the day.
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