I think, in general, Asians would be able to stretch from C to E (1 oct and 2 notes). Unless you are pretty big-sized, your hand span should be able to stretch to more notes.
I used to have this teacher (he's an ang-moh) who could stretch from C to G(!!) That's not the perfect 5th, but an OCTAVE above that!!
Man, his chord voicings were superb, with this kind of hand span. But when I asked him what I could do to emulate what he was doing, he just smiled "pitifully" at me!!
*sigh*
As for Hanon exercises, I used to make it more interesting (for myself at least!) when I play Hanon, by creating variations of it, eg, I would do a SWING version of Hanon, or I would swing the right hand and play straight on the left (or vice versa), then I would play it in a displaced manner (my left hand would start 2 or 3 notes after the right hand has started, and so on so forth!
You could get LOTS AND LOTS of interesting variations in that and it used to keep me occupied (practising Hanon exercises) for hours! :lol:
QF