Well the GTX 470 does not seem bad but only when you OC it and when you OC a GTX 470 it will eat much more. Now if you think about the 25% or so OC needed to reach GTX 480 performance level and the amount of PSU power needed it might not be a bad idea given you have a strong enough PSU.

Alternatively if you think your PSU cant handle a OCed GTX 470 just get a 5870 its as simple as that, as far as temps go i have a open case since 6 years and dont plan on changing it.