Need some info on the new 70-300 IS

I currently have the 75-300 USM "Non-IS"
I've checked the aperture at different focal lenghts.

My conclusion is that the lens is:

f/4.0 - 75 to 90
f/4.5 - 95 to 135
f/5.0 - 140 to 235
f/5.6 - 240 to 300

I want to know the correlation between aperture and focal lenght on the
new 70-300.

Since the old is only f/5.0 at 200mm which is only +2/3 stop difference between
the 70-200 f/4, IS would be more usefull in low light than the constant f/4 from
my point of view.

And I also consider the sigma 70-200 f/2.8. And I only use IS for hand shake.
Stoping the motion is not my priority and wonder if the 3 stop IS would be
better suited for my photography. Size matter too

You can find it at my site here http://www.pbase.com/f​stopjojo/isvf4

Thanks, it's what I was looking...

Damn the choice is not easy...
IS is so tempting...

Go for the IS, you can always put a red elastic around the 70-300