Just read the subject line from the OP on this again. I stick with my opinion that the "Best" size boil kettle for 10g batches is 20G. You can get by and be very successful with a 15G (as I have) but 20G is optimal IMHO. No need for fermcap, standing over the pot like a vulture, constantly adjusting heat, not being able to get a good rolling boil, etc....
Dave