A factory motor is more than fine - depending on the application.
Hence if you tell us how much you have to spend, what your intended use of the car is etc etc - people can help rather than just keep throwing ideas around that might not offer you any real benefit at all.
Stock heads are fine, stock bottom ends are also FINE if you only want say 250rwkw.
So why put forged pistons, rods, N1 pumps etc etc spending cash on the head and all sorts of stuff in there?
All you need is a new turbo, dump, injectors, AFM, ECU, clutch etc - That's 5k just there.
Dont forget suspension, most likely some attention to brakes and then suddenly its 7k-8k-9k