Well,thats a good reason,but,if you are just making fillit welds[not full pen welds in a bevel,] you don't have to worry,that 6013 will give you all the strength a fillit weld will give you if you turn it up a little.Having a fillit penatrate in 1/2 inch will make it no stronger than 3/32 inch,very hard to make two pieces one with a fillit weld,[thats what full penatration welds are for].One way you can beef up a fillit a little is put enough in it as well,[up on sides,might need mulitple passes,one either over another or stacked on another,all tied into each other,etc]
Now if you are doing something more than that[welding pipe full pen],than you gotta get you a dc welder,E6010 is all the rod you need for 95 percent of things than.