If cost is no consideration how good of home A/C can be purchased?

[Faith is Good]

When I had Central Air put in a couple of years ago I said that I wanted an oversized unit for my house. The A/C guy said that giving me a 4 ton when I only needed an 3 ton wouldn't help it get any cooler. Well on hot days when the outside temp gets in the upper 80's or 90s espeically with high humidity our A/C cannot even get the temp below 73 especially upstairs. For some reason it seems to get worse at night just when you would think it would work better. So if I were willing to pay any price could they get me a system to keep my house at a cool 65 even if it got to be 100 outside with high humidity? Could they do it for Oprah?