Hello guys, my $.02 on this subject.
I have been looking at these headers also. I have come to the conclusion that they are not worth the money. They might look cool for a while but they are very poorly designed. The collector sucks, this puts all four primary tube exhaust pulses at the same place to then have to either go up the secondary pipe or revert down the opposite primary tube..... This would explain the experience of extended time to boost threshold since the turbine is not seeing the same exhaust energies it does with the stock unit. The OBX unit is the only one that I have seen on FleaBay that I think is interesting enough to try. However it is a $400 try. Oh and BTW, 304 and 321 stainless steel has 209% less heat conductivity than mild steel. On average it will retain the heat of the exhaust within the interior of the tube better than cast iron. Essentially making coatings a unnessesary addtional expense on stainless, UNLESS you are having trouble with frying things that are near the exhaust. Take a look at most F1 or simular racing engines, they are using Inconel or at the least 321 SS, it is not coated or wrapped in most applications as it doesn't need to be. If it is wrapped Inconel and 321 are about the only alloys that will put up with the punishment.
Take a look at Burns Stainless (
http://www.burnsstainless.com), they have some good information regarding materials and also some very nice collectors. They work, and very well, however they are not cheap considering it would cost ~$350 for collectors (3ea 2into1), then another $150 plus in tubing, ~$100 for flanges, ~275 2-1 turbo collector, then put it all together. This makes for a really nice ~$1000 header when you are done.

It will work substantially better than stock or one of these cheapies, provided it is designed and built properly.
Does anyone know if anyone has Extrude Honed the stock cast pieces?