These are the clear signs of resource abuse
Pretty likely, the program is trying to load too many files at once, and the disk subsystem cannot deliver: it's called trashing where the disk heads are probably all over the place trying to grab all this data at once, attempting to serve all those cores, resulting in catastrophic performances.
The immediate workaround is to reduce preloading in the options (move the slider to the far left) or disable it altogether by unchecking the option, as well as disable parallel loading. With both options disabled, the program will load images one at a time, as fast as the disk can deliver them, and no trashing should occur. Defragmenting, if needed, can also smooth things out considerably.
You can then work from there and re-enable preloading, increasing it in small, conservative steps until you find the sweet spot that matches your heavy files and your disk's abilities.
As a side note, a fast
disk subsystem starts at 300MB/s, as in SAS RAID, and would allow reading a mere 4 files per second given their size. Extra-large IDE/SATA disks are great for archival storage and offer excellent cost/capacity ratio, but are not exactly top performers when it comes to multi-tasking, multi-threaded I/O.
For users wanting to measure the average throughput of their drives, there is the free HD Tune 2.55 utility from http://www.hdtune.com
(scroll down on their download page).