Question: Low light performance comparison between the SX40HS and the SX50HS

I just received the SX40 from Amazon, today, and am seriously thinking about returning it in favor of the SX50.

The only reservation I really have, is the higher minimum aperature of the SX50. Some reviewers on Amazon agree that compared to the SX40, the SX50 is much harder to use in low light situations. One even goes so far as to say that because of this, the camera really isn't a good all-around camera, but should only be considered a specialty tool for birders and other wildlife photographers.

http://www.amazon.com/review/R39AVZ1B09VG8Q/

Can anyone here confirm or deny this?