fyi - GMC Envoy V8 AWD new 2007 ratings are 13/19
Hummer H3 -I5 4WD new 2007 ratings are 14/18

Therefore expect no improvement in gas mileage with V8 H3. But a huge difference in usable power and torque.But that lump of cast iron up front will do nothing for the onroad handling or offroad dynamics of the H3.

Owners of current H3's will end up paying through the nose to trade-up, if you include the $15K loss on a 2006 traded-in.

Later if I want a fast street SUV, I'll consider Ranger Rover Sport V8.