16GB/76hours = 5.05GB/day = 61.2KB/s

From my small study, 3GB of 'new unique content' should saturate an available upload bandwidth of 16.5K/second, making your content almost four times as popular as the norm, although still about half as popular as 'illegal content'.

The wide availability of your CBT files and good naming will certainly account for some of the popularity, as will I'm sure the quality of your offering - kudos to you.