Ginger:
I am glad you already have the Pure Strength series because that has been my mainstay throughout the last year and a half and it has given me great results (I also use MIS and CTX upper body for additional weight training each week). I think that all three tapes of Pure Strength comprise the best and most effective strength training routine you could possibly do.
That being said, I think it is also important to shake things up once in awhile and get away from it. Your muscles get too used to doing the same thing and further development stalls. Also, no matter who great a workout is, it can get somewhat boring if done continuously for months at a time. I believe Cathe had this in mind and created Slow and Heavy for us to use in shorter bursts.
I just finished a three week rotation of Slow and Heavy.
Here is what I found:
Right before I started Slow and Heavy, as I did my last Pure Strength, I wrote down the exact weight I was using for each exercise. I made an effort to use the heaviest possible weight I was capable of using with good form. Using such heavy weights was a challenge for me and believe me, I used the absolute heaviest I could. I was certain after each set I could not have lifted any heavier. I was wiped out after each session, dripping sweat and shaking like a Chihuahua. But this was part of my experiment and I wanted to see (a) what was my heaviest poundage for each Pure Strength exercise and (b) how my strength would compare after Slow and Heavy.
After 3 weeks of Slow and Heavy I returned to Pure Strength and started with the weight poundage I last used. I am glad I took the time to actually write it all down because I would never have remembered exactly where I left off.
I was amazed that although this poundage was still pretty heavy for me, it was nowhere near as difficult to complete the lifts.
So my conclusion is that I did not stay with Slow and Heavy long enough to see actual gain in muscle definition but it sure did give me a boost in strength, allowing me to now go even heavier in Pure Strength than when I left it. This in turn translates to more muscle development down the line.
I think Slow and Heavy is a valuable and valid regimen with great strength gain benefits.
Marlene