region render is not faster?

[Youn]

I have rendered a 3200x2400 image but now want to go back and render a small section that didn't resolve as much. So, I've setup the render region, it's about 330x120 in demension.... it does not render any faster then the entire image did! I started the region render from scratch (instead of trying to resume using the igi) so to compare the speed against the entire image rendering (I had saved the entire image after an hour of rendering then continued... and I am comparing the region render after an hour of rendering against this, they look the same!)

I would expect it would render much faster and also take less RAM. What is going on exactly? Is it still rendering the entire image but only displaying/saving the region?

I am using Indigo 1.0.5...

[OnoSendai]

It uses the same amount of memory, but should be faster.