409 is considered a "second generation" ferritic stainless steel. 409 is lower in chromium and carbon, but have powerful ferrite formers added to the melt. The ferrite former added to the 409 is titanium. Another name for the 409 is "pseudoferritic" because of the additional ferrite former other than chromium. The filler metal used would probably be the matching 409 or 409Cb. I don't think there is a 409 or 409Cb listed in A5.4, though. The only SMAW ferritic electrode for welding the ferritics is an E430, but it does not contain any stabilizers such as Ti or Cb. 309 and 309L are the most common austenitic grades used to weld 409, although E312 and E310 are also used. Now, the choice is up to you..