The Perfect Size

I recently had a test that required me to consume a lot of liquids and to also keep those liquids inside of me for awhile.  I know that's not a great opening line.  However,  it was enough time for me to think about size. Size of body organs, capacity of these organs, serving sizes of beverages, serving sizes of cakes. It doesn't take very long for my mind to circle around and land on something sweet.  And by sweet I do not mean this enormous KFC bucket-like sugar pond.

I was curious to find the largest size fast food beverage after my experience that morning.  This is 64 ounces, or a half gallon. Of course I had to look up the capacity of a human stomach, and then the bladder.  We all come in different shapes and sizes so there is no accurate answer, but I at least know now that I can barely hang on to a 17 ounce bottle of water.  I'm having a hard time picturing someone at a drive thru balancing this on their console, drinking it with a straw long enough to reach the bottom, and consuming it without bursting.
Back to the sweet destination that my original thoughts landed - cake serving size.  In the cake world a party serving size is usually 2"x2" and a wedding cake serving size is 1"x2".  Which explains why at a wedding reception I'm always eating the scraps from everyone else's cake at my table.  I'm sure, like the drink above, everyone has their own preference when it comes to cake serving size.  Even though I bake a lot of cakes and cookies, I don't actually indulge daily with beautiful, nutritionally dead treats unless it's for a special occasion, or if I want to  have to trim your cake to level it.  Somehow cakes and cookies taste so much sweeter this way. So when I do indulge, a 1"x2" piece of cake feels like a prank.
But beyond the size of the slice of cake you'd like to eat, what is the perfect size personal cake? And I don't mean the size that you would eat if you are trying to be "good."
I previously made some petit fours that you can see here.  I would not survive on only one.  My smallest cake pans are 4" in diameter.  Waaaay to big.  Below is an example of my first try at a pretty little fondant ruffle cake in a 4" diameter for a friend.  Also below, very large individual size cakes for a boys basketball team.

Of course the easy answer is the 3 or 4 different sizes of cupcakes that you have to choose from.  I do love a good cupcake, but it's not the same as eating your very own mini cake.