shounak,
no offence by this, but a lot of the times it is the incorporated skill of the driver as much as the actual vehicle's ability.....technically an auto should rip a manual a new rectum, but it often isnt the case, due to my above statement. Vehicle condition plays a big part too, as you would well imagine. Think of it like this, every engine has a peak torque and a peak kw figure, right? these occur at a certain period in the rev range and these are the points that you should be considering to shift at. What is the point in revving past the peak power point? this is where autos get it over manuals most of the time, see in a manual when you put your foot on the clutch, the revs will drop between disengagement and re-engagement of the clutch, this is the time you want to minimize to keep your engine "on the boil". An auto if used properly is far more efficient at shifting than a factory manual. This is just scratching the surface, but if you go and get a dyno power readout, use that to your advantage and plot your engines peak power points.
