I have two 5500 SS elements in HLT from bobby. i have tested my system with 20gallon HLT and both elements on with my 50amp control panel. So far with my testing i have not had issues. you should be good with running two. I went with two elements in my HTL and one in my boil kettle. The reason i only use one in my BK is that it will be getting wort at 150+ so the time to get to boil will not justify having two elements. here is write up of my control panel..
http://www.theelectricbrewery.com/forum/viewtopic.php?t=27904
at the bottom of my post you can see that with both of bobby's elements they are pulling 44amps.
if you are building your panel go with DIN RAIL !!! it makes your life much easier i think.