In addition to Jason's list of potential issues ...
- number of stripes used for loading, especially if compression is involved (dumping/loading compressed files can require a good bit of cpu; a high(er) number of compressed stripes could lead to cpu starvation on the host as too many processes fight for cpu time)
- disk IO contention ... not only on the filesystem/disks where the dump files reside, but also on database devices (the sybmultbuf/write process is dumping a large volume of IOs onto the database devices; if those devices are (relatively) slow and/or being heavily hit by dataserver activity, then the loads can be delayed due to IO contention on the database devices)