An idea that just occurred to me while reading this is that shelving racking, such as you see in most shops, would be ideal for this situation. I have some shelves just behind my desk mounted on this type of racking which have steel bars about 3/8" wide and are about 6ft tall screwed into the wall every foot or so. I believe the length of these would counter quite a lot of the bending stress (although thats not really my field) and as a fringe benefit they have mountings which the shelves hook into every 1 1/2" or so, this could even allow the desk to be lowered to a normal seating position with a little work. Also, I think that any failure of this type of racking would be fairly gradual.
I've been using precisely that solution for several months. It's perfect, and I have absolutely no worries about weight, because there are several screws along the length of each bar. My laptop and monitor go on one rack, and my keyboard and mouse are on another, about a foot beneath the first.
Similar to what is shown here http://www.richardsonsuk.co.uk/product.aspx?p=46 (no affiliation, just the first similar looking thing I came across on google).