My opinion is unless the pipework is of a decent wall thickness (ie not 1.6mm thick like most cheap brands) then it WILL crack eventually. I've had to re-weld up numerous stainless headers after they crack and even if I purge weld the pipe they still crack afterwards. If your set on stainless headers, then go for steam pipe, thay may be heavier but will not crack. Another note is if you have an external wastegate hanging off the side of the maifold make sure it is securely braced, cos I'll guarentee that'll be the first place it will crack ( because of the weight of the wastegate bouncing up and down it will put strain on the pipe weld) Also if theres a choice get 316L grade s/s instead of 304L grade s/s. It can take heat shock slightly better than 304L. So if it was me, unless the stainless manifold was made from steam pipe and has bracing I would just stick with good old mild steel ones, they may not look as shiney but in the long run they will cause you less grief.