UPDATE: My HDs arrived a couple of days ago and because I was busy with work I had to wait a couple of days before I could install them, so they went in this evening. My first impressions? As a baseline to begin from, I installed them at the same height that I had the Crawlers to and gave them a go but wasn't too impressed - the neck was good but the bridge was very mid orientated with very little lows or highs, so I raised it up a couple of turns and bingo, sweet spot found! I agree with the comments above about the pickup height, although the neck sounds best some distance away from the strings (it worked out to be more or less the same distance from the strings as with the Crawler neck), the bridge needs to be a little closer. I'll write a more detailed review and comparison between the Crawler, Nailbomb, Rebel Yell, Mule and HD sets in the same guitar at some point in the near future, but the quick version is that having found the optimum heights I'm very happy with the HDs - the bridge has just enough of everything (top, middle and bottom end) and also has just enough grit to keep it interesting. It has a little bit of all the pickups that I've mentioned - which is basically what I was after, although it probably has less of the Crawler than I was expecting. The neck's tone is similarly sensitive to height, with more mids coming in as you get closer to the strings, but backed off so that it's about flush with the pickup ring, it scoops the mids out a little leaving a nice clear metallic attack at the top end and a nicely rounded bottom at the other. So despite not being impressed at first, after some fiddling around with heights my impression changed and I now think that these could turn out to be a very good choice for this guitar.
