Ive started making log manifolds for my NC using 1 1/4'' primaries into a 2'' log, with nice sweeping entries into the log etc.. material is 2mm thick mild steel. Is it going to be strong and durable enough for a turbo application, or should i be using buttweld fittings (steampipe), and if so, should i use the standard thickness or the extra thick bends?

I'd use the steam pipe, just the regular thickness no need for extra thick.