Don't do it! Get an IC-60.

SWCG cost does not go up in proportion to capacity; but SWCG life is directly proportional to on time. The larger unit will last longer.

By the way, if you get an AutoPilot or Hayward Goldline unit, I believe you can turn down feed rates much more. With the IC series you only have a 5 step adjustment (20-40-60-80-100%).