Hi, and hmmmm...
I have a "dark sounding" CIJ Strat - alder body, rosewood board.
I had trouble getting enough top end bite out of it with both ITs and Sultans. I didn't know quite how dark it was until I got a couple of Roadworns and put the pickups in those...
Like 38th, I was going to suggest Mother's Milks, but I haven't tried them. I strongly suspect that Mother's Milks is the brightest option (ITs have extra mids I believe) - mebbe ask Tim about this - but you're using them already.
In the next couple of weeks my CIJ gets the Sultans back (the 50s Roadworn gets Apaches) - it wasn't the tone I was originally reaching for, but it is a lovely tone I can use and would like to explore, and the other guitars do produce the tone I was after... (There is a later option of switching things around again and trying Apaches in there - but that's after I find out what they do to the Roadworn...)
I'm also going to replace the CIJ's bridge assembly with a steel one (or possibly just the trem-block). That should give me a bit more, and I'll call it a day on that one and start loving it again just as it is...
My gut feeling, from all this, is that you're not going to be able to brighten up a dark strat in comparision to another strat with BKPs alone. ITs didn't do it for me, Sultans didn't do it for me either (they're as bright as ITs but sweeter).
BKP's really bring out what the guitar itself brings to the party. I've personally found this really shows on strats - two guitars, one dark, one bright, sounded HUGELY different with the same set of BKP strat pickups. When I started checking it out, I found the difference is already there, unamplified - I just have accept guitar A does not sound like guitar B.
However, I have learnt some stuff over the last couple of years. Here are some other guitar-based things to look at that might squeeze a bit more brightness out:
Yes, pickup height - further from the strings is clearer/skinnier. And angling them higher on the treble side can give a bit more brightness.
Assuming it's a trem guitar, try taking the backplate off. That can sometimes make a difference, no idea why.
What is the bridge assembly made of? I didn't believe in this until recently, but a steel block does actually make a difference.
What's on the back of the neck and how thick is it? I stripped mine and the guitar got a little more airy (this was a bit of a surprise - I did it without even slackening the strings, so it wasn't a "new set of strings makes me think my tone changed" scenario :lol:)
Start fiddling with the potentiometers and tone capacitors. If you've got paper-in-oil (PIO) caps, take them out immediately and put bog standard ceramic caps in - in my experience that brightens things up a little on a dark guitar (if you don't fancy those, try orange drops - they're not quite as "smoothing" as PIO). Also experiment with the cap values - some folks are convinced that this has far more effect than what they're made of. I've tried .022 (as used for humbuckers) and .033 instead of .047 - I don't really like how the tone controls behave with those, but they do make you feel like the guitar is a touch brighter. Also, try pots with higher values - not tried this myself yet, but I suspect it might do something...
Anyway, welcome to the forum :D and good luck. Hope you get sorted, it's been bugging me for a couple of years!