I have a dedicated sample drive (SATA 600) on my fast desktop (core i7 4.3 GHz overclocked). It takes about 30 seconds to load the Soniccouture Array MBira preset into Kontakt 5. It is about 4 GB in size. The drive is defragmented.
On my laptop (Core i5 - 1.8 GHz) I have a 1 TB SSD. Running on laptop battery power that same preset loads in 3 seconds.
When I run one of the monthly updates to Sonar, the laptop installs the updates much, much faster.
I heartily recommend an SSD.
Just think for a minute - no matter how fast your system, a hard drive is spending a lot of time moving that read head around. No data is read or written during that time, which is an eternity to a CPU.