Thanks for your support and encouragement - great to hear you're a RuneQuest 6 fan also!
There were lots of reasons for choosing RuneQuest 6, but ultimately it was down to how sophisticated I felt the rules were, and how much I could do with them without having to write lots of rules additions for the game - I'd like the Chronicles to be as much setting material as possible, and be relatively light on the rules. RuneQuest 6 has some great personality and augmentation rules, plus the creature abilities, fighting styles, special effects, and all the various magic systems give me a lot to play with. I think it accommodates the greatest range of styles of play out of all the d100 sets - you can play it pretty simple and stripped down, or dial up everything for maximum breadth and crunch.
Ultimately I felt they'd be the best fit for Chronicles for the way I play it. At the same time, the fact that we won't have to include lots of new rules means that people should be able to take the book and play it with exactly the d100 rules set they like to use.