I know the connectors you are talking about but am not convinced they are much stronger and also they are $$$... Do you happen to have any pictures of the sleeves? Are they just 2 halves of a larger tube that have 1 bolt going through each side of the 2 sections of cage or what?
Also I am planning on having sandwich plates which will hopefully be tied into either the sliders or frame. My goal really isnt just to be protected in a low speed rollover on the rocks, but actually live if I do get into any kind of accident on the street since the likelihood of me going on my lid is pretty high. This is why i am so concerned about these stress issues.