Central, The way they do the ratings is to rate them at the average voltage over a usable range of voltage or use. For example as you said, your pack charges up to 8.3v, but when you run it it starts to really die at somewhere around 6 volts. So if you average the two you get the voltage rating. This isn't exactly how they do it, but it's the same idea. Alkalines are somewhere around 1.6+v new but they rate them at 1.5v.
By the time they get to 1.3v or so they are usually gone. Nicads don't have the voltage that alkalines have, but they give incredible amperage. Hope this makes sense. Joe