I'm actually in the middle of selecting my fans. I started by sponsoring some fans for a test by Martin, and then buying at least one version of some others that he had already tested. I ended up with 11 or 12 fans that I started auditioning on my rads here at home. Here is a shot of my laboratory.
Hooked them up to a fan controler, and spent the better part of a week just listening to them at different speeds. I'd turn one on and another off at the same time to hear the differences. Some fans sounded a lot different on the rads, vs off the rads, so you're on the right track by evaluating and making your decision separately for case fans and rad fans. I'll be posting a separate thread documenting my evaluation and notes on the different fans, but I'll give you a preview of my take on the GT AP-15's. When spinning at anything higher than 1,500 rpm's, they made a lot LESS noise than anything else in my test. BUT....for me at least, it was about HOW they sounded, instead of how loud they were. I can't stand the sound of the GT's when compared to other fans. More of a mechanical hum with a kind of high-pitched ball bearing squeal. With most other fans, the mechanical hum is lower pitched and kind of drowned out by the air noise. GT's sound different than any other fan. And I don't like them. But...they are quiet. Just make sure you are ok with how they sound. Some people may not even hear the same stuff I do, because everybody is sensitive to different frequencies.
I'm leaning toward the multi-frame Noiseblockers, but the SilenX fans also performed awesome-ly.
Subscribe my build log and you'll get a link to the fan round-up thread and updates on my fan decisions. Good luck with yours!