I've been running a pair of 729's in the alps + uk Dh racing for a couple of years now, they're still straight, i've never touched them with a spoke key, so i figure they're over-kill (for me).
this year i'm taking out a set of old 721's, they've seen even more action than the 729 wheels, and are only just out of true.
the 721's are 100g lighter (each) than the 729's, yes, i'm a geek with a set of scales…
(and my bike's got plenty of travel, so the wheels are saved from a lot of the forces)
for a goodncheap option, how about the halo freedom wheelset? – i've got a pair of those on my play/jump/learning-to-do-tricks bike, and they're plenty strong enough. Cheap too, the only downside is the 500g rear hub – a hope proII weighs 300g