EMS powered might be okay these days but a year or two ago they were ****e. I have bought products from them like 4 years ago without an issue but based on everything that happened in recent times I would stick clear. The turbo kits from KO,ATS and Berk are top notch. My gt35r kit was from KO and it was awesome.Dylmrt uses a Berk kit.
With the exhaust manifold an aftermarket one will flow better. But the stock one is uber strong and will not crack and has been used on 600hp+ engines. If you have a look at the kits from the three suppliers I listed they all use an adapter on the stock ex manifold to suit the new turbo. So yes you can spend $1000 on a new ex manifold and make a bit more powerbut run the risk of crack in one of the many welds and have to remove it for repair.
In saying the above some manifold munufacturers like Full Race in the US warranty their manifolds against cracking etc. But they are probably the best quailty for the 3sgte and cost over the 1K mark I think.
I don't have anything to back up my comment on the dyno power measurement difference between dynojets and dyno dynamics machines. Its just common knowledge that Dynojets seem to read higher than dyno dynamics.
Any kit with a decent medium size turbo, injectors, aftermaket ECU, exhaust, IC, cams, full engine build will make high 200s. Also know that US 93MON fuel is the equivalent of 100RON here. Different octane measurement method.