Sometimes the references to read noise in the product descriptions are confusing. Some products refer to the read noise at a high gain setting and others to the read nose at a low gain setting. If you don't look at the graphs you might make the wrong choice. If I am interpreting the significance of the graphs correctly you want the product with the lower read noise at a high gain setting if image under dark skies; you want the product with the lower read noise at a low gain setting if you image under light polluted skies. I'm assuming you will need to use the low gain under light polluted skies to increase your exposure time to collect enough signal.