Yep, I'm intrigued - what do BKP recommend?
Anyway, at least this thread has helped start me play guitar again!! I've been stopped for a good few weeks, kinda stalled between what to play next... This thread and the arrival of my Deluxe 40th Anniversary Boxed Set of... Irish Tour '74 has helped me stick one of my trusty strats on.
I've got ITs, Apaches, and Sultans. The first set I bought was the ITs and I was in roughly the same boat as you. The 59 set didn't exist, so I was thinking "it ought to be Mother's Milks but I have a hankering for ITs".
I went for ITs. It was actually the "wrong" choice for that guitar (a CIJ "62") because the guitar itself is quite "mellow, warm and rounded" sounding. Like Telerocker says, the ITs have more mids and low end than some, so in that guitar I couldn't get the bite and lightness, the transparency that I wanted sometimes - even with rolling off the volume. They've been in a 60s Roadworn for several years now. That's a very lively and resonant strat, and the ITs do EXACTLY what I want in it. It absolutely nails the Rory on Irish Tour 74 strat sound. But when I roll off, it's still a harder, middy sort of sound. That's fine with me... but I can't quite get that gorgeous lightness and melodic cluck of Steve Gaines or Ed King with it. It's possible that I could at a decent volume, gigging with a drummer volume, but I have to play quieter nowadays(!) so I'll never know.
I would say that if you value that "lighter", "sparkly with body" sound, then you should err on the side of caution and go with the 59s (or Mothers Milks) and rely on your boost or whatever to give you more meat when you need it. I'm probably going to try a set in one of the other strats soon.
But if, like me, most of the time you want that more robust bluesy and biting strat that cleans up nicely with the volume control and scrunches like an SG when you need it... then the ITs are for you.