Here is a descent breakdown of the different uses for the Permatex line AND some mention of Loctite 5900: http://www.v8buick.com/showthread.php?t=97537
We put a steel fireplace box & ducts in our house and we had to use a silicone adhesive. It was good for 1000 or so degrees. I looked on-line and could not find the name of it, but I will try to find it at home. Below is a link to some other high temp adhesives. Also : http://www.cotronics.com/vo/cotr/newprod.htm