I think that you need to go to JDM Anonymous!! I don't even know what an HKS manifold is. I have not seen one Evo with something that was called an "HKS manifold," so I can't tell you anything about it, but I can guess that it's quite expensive and doesn't provide much gains.
There is only one aftermarket manifold that has proven to make more power than a stock manifold that has been ported and coated, and that's the $900 tubular Full Race manifold. It made 4whp more than the stocker without losing any torque or spool. All others made less power and/or torque while costing more and being prone to cracking due to thin stainless steel walls.
i have a 2nd hand Megan, and its been doing fine.. been on for about 4 months now. no problems. Only that some of the Coating has come off though. Got alittle better Spool out of the turbo, but not sure of the gains, have not dynoed my car yet.
Warrtalon, is there a certain company or two you've had succes with on the porting and coating of the manifold? I would think a competent machine shop/engine builder would be able to do it and then you could get it high temp coated from a number of places. I would think if someone with some porting knowledge could get hooked up with a reliable coating service they could have a nice little side business. It seems pretty obvious the stock piece is a pretty tought cookie and with some porting can be of pretty good benefit for not a lot of $.
Yeah, Buschur. They have been doing it for a long time, and they specialize in it for the Evo. That's pretty much where everyone goes. Yes, there are skilled craftsmen all over the country who can port things and others who can coat things, but Buschur gets them both done right there (their ceramic coater is down the road) so that you get it all done at once. They also do an exchange system to minimize downtime. What I did in order to reduce downtime to 0% is I bought a used stock turbo set (exhaust mani, 10.5 hotside, o2 housing), then sent it all to Buschur. They immediately sent me back the same parts that were on the shelf pre-coated/pre-ported, and I had them back 4 days after sending the shipment. I then installed those parts and sold the ones that came off my car. My net expenditure was $0 due to the parts being part of my sponsorship, and I had no downtime.
The main reason I'd suggest going to Buschur as opposed to a guy down the street is because they know exactly how much to port, where to port, where to gasket match and what not to port (e.g. runners on head side of mani). I wouldn't want someone just randomly gutting it out without knowing exactly what works best on the Evo.