An 8 oz. candle has about 32 hours of burn time, assuming it burns 4 hours at a time. The wider the candle, the less time it will burn. This means that the metal candle will burn a little faster, but throw more scent.
All of our wicks are designed to burn the entire candle. However, some of the wider ones need more heat to burn. You'll want to let 'er rip until the entire top layer of the wax is melted. This could take a couple of hours.
If you're in a really sticky situation and there's a big tunnel, hit that sucker with a blowtorch or something to melt it down and even it out... The wax melts at around 120 degrees F, so you don't need much heat.
As the wick burns, it turns to pure carbon and sometimes falls into the wax. It doesn't really affect anything, but if you're not a fan, you'll have to trim the wick as you go. Once you're done burning it, trim the wick down to about 1/2 inch.
Volume is an incredibly difficult thing to judge. Humans are super bad at it. All of the containers have been volumetrically measured, and they are, in fact, the same size. However, do keep in mind that the wider the diameter of the candle, the faster it will burn and give off scent.