Keep in mind I don't own either S&H or PS anymore, but I've viewed each of them in the past, so with that in mind . . .
I think you'd get the best variety at this point if you got Slow and Heavy, primarily because the reps are . . . well, much slower, distinctively so, and is designed to offer premium strength gains. The slow counts of the reps are S&H's prime (but not only) difference with Pure Strength.
Also, there is more fully balanced core work in the Slow and Heavy Series, incorporating planks, "supermans", long-lever leg and arm positions in the abdominal segments in addition to traditional ab work, which is again distinct from Pure Strength.
Also, as I recall the Slow and Heavy series offers segments on wrist and forearm curls, an often-neglected set of muscle groups whose strength is necessary to continue building strength in all of the other upper body muscles.
Just my $.02 - and I haven't owned SH for over a year now, so my memory may be a bit faulty.
A-jock