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.
No they are a 3"-4" peice of tube that you just slide over the joint where the two cage peices but together, not a split peice of tube.. You want to use a size that is pretty snug on the OD of your cage tubing. Then you just run a bolt through each side. I'll try to get a pick, but mine is all taken apart right now for my 4Runner build. I think you are stressing out on it a little too much.
Just having a decent cage made of good DOM material will be vastly more protection than stock. A buddy of mine just had a BAD roll over in his YJ. He had a really crappy cage made of the stock rear roll bar and some front runners made of HREW mild steel with the ends just tacked to the rusty floorboards. Despite the lousy engineering the cage worked and he walked away with only bruises.
I think it qualifies as a high speed multiple roll over. Here is the link:
http://www.youtube.com/watch?v=g4rY7Y6wgYA&feature=related