It's literally years of work (search, download and hoarding).
One I'm struggling to get since years is the "Cum candies and piss panties". No luck so far and it's only in the retired pack at $449.99, obviously I won't waste that amount of money for one single video missing (still looking but I don't have my hopes high for this one).
It's only slow from certain CDN servers. I'd suggest if you get a slow download, remember the CDN server number, refresh and try again. If you get the same server, roll the dice again.