I've read that 304 is supposedly superior to 409 Stainless steel. Is there any truth in this. What are the main diffs between the two? For me right now its the difference between a $1200 and $1600 header system. Both are respectable brands.

 

The info is correct. "409" stainless has a higher carbon content & actually rusts. Now don't fret too much about it if you are not concerned about appearances; it's not going to rust badly or rust through like regualr steel tube. It's more of a "looks" rusty.... IMHO