If you read my other posts on the subject, you'll see that a 6 oz coffee has roughly the same amount of caffeine as a shot of espresso. Perhaps in the days when Robusta was the primary source for drip coffee you got more caffeine, but those days are long gone. Caffeine can be extracted from coffee in a very short time given a good pump espresso machine and proper technique. If the wrong beans are used, and the technique is lousy, then yes espresso will have very little caffeine content. The extra "stuff" you refer to is bitterness which happens with drip extraction. The bitter flavor has little to do with caffeine and more to do with other byproducts which are produced by overextraction.

The ultimate for me is a double ristretto with a cube of cane sugar and perhaps just a drop or two of half-n-half if it's early in the day.