Noticing all the numbers, I had to make mathematical sense of all of this.
Based on searching the amount of caffeine in one shot of espresso (https://www.google.com/search?q=caffeine+in+a+shot+of+espresso&ie=utf-8&oe=utf-8). I determined that:
One shot of espresso has 64 milligrams (mg) of caffeine per 1 fluid ounce (fl. oz).
That would mean that one 16 fl. oz of coffee would contain 5 shots of espresso.
320 mg of caffeine in one 16 fl. oz drink / 64 mg of caffeine in one shot of espresso = 5 shots of espresso in one 16 fl. oz drink.
Based on searching the amount of caffeine in one can of Red Bull: (http://www.caffeineinformer.com/caffeine-content/red-bull)
One 8.46 fl. oz of Red Bull contains 80mg of caffeine. To reach the amount of caffeine in a 16 fl. oz drink from Starbucks, you would need to consume 4 cans of Red Bull.
320mg in a 16 fl. oz drink at Starbucks / 80mg in an 8.46 fl. oz can of Red Bull = 4 cans of Red Bull.
In retrospect, that seems find until you understand the fact that one 8.46 fl. oz can of Red Bull contains 27 grams (g) of sugar: (http://tracker.dailyburn.com/nutrition/red_bull_red_bull_250_calories)
If you were to consume the same amount of caffeine as a 16 fl. oz Starbucks coffee, you would ingest:
Four 8.46 fl. oz cans of Red Bull * 27 g of sugar per can = 108 grams of sugar.
If you were to order a 16 fl. oz drink from Starbucks, in this case a Caffè Latte (http://www.starbucks.com/menu/drinks/espresso/caffe-latte), you would consume only 17g or sugar. That is clearly a better option even with the higher amount of caffeine.
TL;DR:
-A Starbucks Grande 16 fl. oz drink contains 320mg of caffeine and 17g of sugar.
A 8.46 fl. oz can of Red Bull contains 80mg of caffeine and 27g of sugar.
You would need to consume four cans of Red Bull to reach the amount of caffeine in one Starbucks 16 fl. oz drink.
That would result in ingesting at least 108g of sugar.
Edit: thank you to whomever pointed out the error for the amount of caffeine. I deleted that part. Otherwise everything else looks fine.