hey there merk,
this may be off topic, but as a someone who appreciates great singing ability, thought you might wanna check this guy out, if you haven't heard of him already.
http://en.wikipedia.org/wiki/Tireh ... check out the audio samples, has a pretty damn good whistle register (can do it with vibrato aswell). If you can possibily find a copy of 'power of love' (it used to be in wikipedia but now it's gone) you should definitely check it out. this guy has one of the best head voices i've ever heard. not just incredible range, but maintains amazing tone and power. awesome stuff.
let me know what ya reckon.