I believe in my area the problem with lights dimming when large loads such as A/C kick on are coming from the Utility side. No matter how large the service is you would still have the problem.
I had a customer who had a 125 amp service. All appliances were gas except for the A/C Unit. His lights would dim when it started.
He insisted that he needed at least a 400 amp service to solve the problem. The house was less than 3,000 sq. ft. I did a load calculation and found that the 125 amp. service was large enough. I convinced him that a 200 amp service would be plenty big enough and he went with the 200 amp service.
I explained to him that his service size was not causing the lights to dim when his A/C kicked on. It was the utilities supply that was the problem.
