Depends on what the EOR is saying this thing is going to be exposed to.  What are you using for a process to weld these together?

Depending on the service temperature and cycling, 309 or any austenitic stainless steel may not be a good choice due to differenced in the coefficient of thermal expansion.  A nickel based or even a Cr-Mo electrode may be a better choice depending on the welding process (and thus dilution), service environment, PWHT cycle (which is needed with 410), thicknesses, joints, etc.