I really love my new Yo-Yo DESK®. I chose the Yo-Yo DESK® 36 because I have 2 monitors and I needed the extra space. It is 35 ¼ ‘’. wide and fits perfectly with workstations using double monitors or when placed on a standard sized desk. I am sure it will perfectly accommodate your iMac + 27" cinema display + a 3rd display.
Why not make the standing desk on your own. It will be easier to meet your requirements if you will construct such a desk. You can do it following different guides for standing desk DIY with images, for example at GoStanding or HealthLine. Think about this as it is the best way to get the desk with your dimensions