A note about drinking:
Dwarves only eat about 8 times a year, and drink about 18 times a year. In order to scale that up to what they would really be eating/drinking, you have to accept that they eat and drink unusually large amounts in a single sitting.
Also, barrels do not cap out at 5 servings of alcohol. Barrels simply get filled with 5 units of alcohol
per unit of food in a stack that is brewed, which means that a 5 unit stack produces 25 alcohol in a single barrel. Even then, the only reason barrels do not hold more is that stills only accept empty barrels. Barrels do not currently have defined limits, although most containers tend to stop at 10 of whatever objects they hold, regardless of the volume those objects may take up. (Such as bins holding 10 breastplates or 10 earrings before becoming full.)
Regardless, if we are talking about making full "taverns", there are threads that do more thorough jobs out there:
http://www.bay12forums.com/smf/index.php?topic=60681.msg1371687#msg1371687and, if you
really want to solve the problem:
http://www.bay12forums.com/smf/index.php?topic=61620.0i want it simple, so it coul be added fast, not some fancy smancy extra large keg just because it has more style... because that would never be implemented then :/
It's not like Toady has a habit of adding in small things faster than the big things, as far as I have seen...