Aftermarket Exhaust manifold

From MR2 tuners findings on MR2 manifold flow, stock manifold works well below 350hp, light porting helps if you can be bothered (tools under $150 and takes a good 8 hours).

Stay away from eBay manifolds, especially the loop tube style - engine bay heat is nuts from them and even after repairs and rewelding they cracks cracks cracks.

Limit heat - Keep the stock heat shield on the manifold! If u have funds preferably ceramic coat dump pipe or custom heat shield for the dump pipe.

Quality manifold makers like doc racing or full race, from the photos I would guess they don’t match Berk dump pipe etc - however you would need to contact overseas suppliers ATS Racing or Full Race, or Australian supplier like Gorrilla Industries.

Save your money and keep the stock Ex manifold. It is strong and reliable.
 
My previous SW20 was putting out 320KW wheels with a stock Ex manifold. 

IMO Reliability, best flow under 350hp at the wheels (aftermarkets have bigger long runner manifolds that increase turbo lag slightly as much larger air volume to fill/pressurise), best control of killer temps, easiest removal etc - all hands down best is the stock manifold or stock manifold with slight porting/port matching.

Aftermarket quality manifolds are about $1600+ and have no gains from the description of your application.

Dump pipe and exhaust, intercooler and piping, fuel pump, bushings, many items have benefits to upgrade / aftermarket, factory manifold is best. Only time manifold should be professionally upgraded when flow restrictive (when above 350hp). If you have cash to spend, better spent on other items.