If you don't have a very specific, obvious use for the SSD as a data drive (for example, using it to host a heavily used database where access time and concurrent I/Os per second are critical), then use the SSD to hold the OS and as many applications as you can put on it. Using the SSD as a generic data drive is almost always a waste of its capabilities.
to me the main advantage of SSDs are not their speed but their access time , so i would go for the 600 GB one
i have an OCZ Sata III SSD with a supposed read speed of 500mb but i can hardly reach 320~ using HDTune tests
put ur OS on the SSD + games for faster loading times