I don't believe I am slowing down the generation process because as seen in my original post vanitygen can only "find" so many addresses per second, even using a prefix of 1 (all bitcoin addresses) it still only "finds" ~ 0.4% of the addresses generated. I believe I am going to have to implement address generation directly within PHP using something along the lines of Zamgo's PHPCoinAddress.php https://github.com/zamgo/PHPCoinAddress/blob/master/PHPCoinAddress.php and see if I can't speed up the process of address generation that way. Even if I can get it to iterate at about 500 address per second it would be generating faster than vanitygen can "find" addresses.