OEM header performance?

[Pergatory]

Hi all, I have an S13 blacktop and the turbo began spewing oil so I am in the process of replacing it and upgrading a few bits in the process. As I discussed this with a local Nissan shop which seems to really know what they are talking about (UP Garage in Washington), he is convinced that the OEM header is better than a 'cheap aftermarket' header.

Current mods:
Koyo alum radiator
Flex-a-lite dual electric fans
Greddy FMIC
Greddy intake manifold
3" test pipe
Apex cat-back of some kind (deafening)

Mods being installed in this round of upgrades:
GT2871R turbo (.64 turbine)
Greddy turbo outlet elbow
HKS SSQV recirculating
Apex AVC-R boost controller
Walbro 255 pump

As you can see, I'm slowly building toward a well-balanced engine looking for around 300-350hp to the wheels. My most important thing is not to lose response in pursuit of top-end. The header I'd picked for this round of upgrades was a Megan Racing header, I'm sure you're all familiar with it. It's cheap, and wasn't necessarily a permanent solution but I cringed at the thought of putting the nasty corroded OEM header back on. UP Garage is adamant that this is not the case, and that the OEM header will actually outperform the Megan Racing one (with worse top-end, but slightly better response/bottom-end & heat retention).

Ultimately I will probably end up with a more pricey high-end header, but right now I just miss my Sileighty and want it running again. So it's apart in my driveway, and I have two headers in front of me (OEM and Megan Racing). Thoughts? Anyone with direct experience switching between these two headers without changing the rest of their setup that can give me an idea of what to expect? Am I better off just doing it right the first time and picking up that ultimate HKS or Peakboost header right now? Do even those sacrifice response over OEM and if so, how much? I'm kind of going in circles in my head and need some advice to straighten myself out here.

Thanks a bunch

[golfer17]

I'd be inclined to agree with him. Especially for those on stock turbos. I've had a good ss tubular with header wrap on my car and the stocker with stock heat shield, and I prefer stock because it's a hell of a lot easier to take on and off, and also, the stock manifold is divided for scavenging. Personally, I will probably wait until I go top mount/external wastegate before I swap out the header, but there is a chance I might put my old tubular mani back on when I swap my built motor back in and start running 20+psi (2871r .64). I never did run the ss tubular mani on very high boost for a good comparison, but I think Full-Race might have seen some good gains from their bottom mount manifold though, so you might check their website to see if you can find a dyno graph.