My riding position is quite upright all of the time, but I have found on harder climbs that it does help for that last bit if I lower my body a bit - closer to the boobs to the tube position. My bike doesn't have road bars, so I probably do this different than others. I have noted that for some reason when I do this if my legs were burning that it decreases and my breathing gets a little easier.

I am unsure what causes this - but as tall as I normally sit in the saddle it may be that this moderates things just enough to give me a LITTLE more aero position without restricting my airways.

The decreased quad burning is of most interest - I can't explain it, but it works for me.