I am no expert but I just went through the same thing. I got the IC40 for a 15-20k gallon pool. That way I can use the cell on low and it will last twice as long as the IC20 on high.

Got the IC40 with generator on ebay for around the same price as what you are quoting for the IC20.

As far as brands go. I went with Pentair because I have the Pentair Intellitouch controls already.