I have a Kensington 8 (the eight speed version) and the rear rack so far has held up fine. I've toted panniers full of canned food and it didn't creak one bit.

The 8 speed has suited me fine, the one problem is sometimes when I hit potholes or bumps too hard, it shifts spontaneously, and then I have to shift up and down and move my pedals back and forth to get it to work again. I think it's something in the shifter up at the handlebars, but so far all the videos I've found about nexus 8 shift cables deal with the hub end.

I just replaced the stock kickstand with a double kickstand. One of the best things I ever did, it stays rock steady now no matter how much of a ****er I am while I'm loading it up.