Greg G,
I have to both agree and disagree with you. You are right when you say that either wire will work for this situation. However, the ER70S-6 is the more fluid wire. The ER70S-2 is a triple deoxidized wire with a more sluggish puddle, which make this electrode useful for welding out of position. The ER70S-6 is a highly deoxidized wire, containing large amounts of silicon. It is the silicon that increases the puddle fluidity. If you would like more proof visit esab or any filler metal manufacturers website.