I had a clip stop downloading halfway once. It said it was downloading, but it wasn't going anywhere.
But luckily, I always keep the Download Page open until the Clip is Finished. And I just stopped my First Attempt, and just started it again. And it downloaded no Problem. (The Link stays active for I believe 48 Hours after a Successful Purchase)
So whenever you make Purchase, keep the Page with the Download Link open until the Download is Finished.
Aside from that one little incident, the Speed has been just fine for me. I think the Longest time it took for me was a little over 10 Minutes. But that Clip in particular was over 500 MB in Size. Other than that, everything else take no more than 5-7 Minutes.