Not looking good for the 150-500 to be anywhere near the Bigma,,, such a shame...
I put the MTF charts side by side and its apparent the Bigma will still reign...
http://i33.photobucket.com/albums/d73/Telecorder/Bigma-v-150-500-MTF.jpg

http://www.sigma-photo.co.jp/lens/tele/150_500_5_63.htm
http://www.sigma-photo.co.jp/english/lens/telezoom/mf50_500_4_63.htm

DPR's mikeyyy wrote:
> Updated mtf charts
> http://www.sigma-photo.co.jp/lens/tele/150_500_5_63.htm
>
Thanks, Mike...!
FWIW-->
Apparently, Sigma had posted the wrong MTF charts for the 150-500 as incorporating their new posting versus the Bigma charts now reflects the following...


http://i33.photobucket.com/albums/d73/Telecorder/1Bigmav150-500MTF.jpg


After Mikeyyy pointed this out, I did a bit more reading of info on reading MTF charts and now have to say that this more in depth understanding and with the new charts, I'm changing my opinion to be more slightly optimistic about the 150-500.

Paraphrasing Canon's guidance of how to read the above MTF chart, as I now understand it--
The upper Red lines refer to a spatial frequency of 10 lines/mm (equates to Contrast or how accurate a lens' senses differences between similar shades)
The lower Green lines refer to a spatial frequency of 30 lines/mm (resolving or sensing of sharpness of fine details)
A solid line refers to sensing of lines parallel to radius from center ___ (S curves)
The dotted lines refer to sensing of lines tangential to radius ||| (M curves)
Above chart values refer to maximum aperture (most all lenses usually benefit when stopped down)
The contrast curve (upper) is the most important when evaluating differences in lenses and liklihood a lens will be a good performer

The closer the S and M (dotted curves) curves are in line, the more natural the blurred image becomes (more pleasing Bokeh).

An MTF value of 0.8 or more at 10 lines/mm (especially the Upper/Contrast/Red) curve indicates a superior lens; 0.7 -- good
An MTF of 0.6 or more at 10 lines/mm indicates a satisfactory image.

Since most of us use crop factor bodies, such as my D50, any part of the curve on the right - past ~14-mm distance from the center of the lens, is irrelevent -- as this portion is for the edges on a 35-mm FF sensor and is cropped on a crop sensor.

In the above charts, I note that the 150-500 has about equal values for the upper contrast lines and slightly better values for the resolution/lower curve. I placed colored dots on the corresponding values between the two lens for easier comparisons.

All in all, the newest calculated MTF values would seem to indicate that the 150-500 lens may have as good of an IQ as the Bigma; perhaps better when stopped down...

Real world, hand's on reviews will tell the true story...