small SSD
Think of the small SSD as a large cache. Every time your computer accesses data, it is copied over to the SSD. If you are accessing the same data over and over, then that is going to be pretty quick. Thats exactly why it would speed up the OS boot times, as pretty much the same files are always accessed at boot time.
Just remember, the SSD is only 4GB. Larger games are going to be left on the 'normal' part of the hdd. I think for your purposes, you would be better off investing in a fast hard disk, or consider two smaller disks and put them in raid 0.