Nickson asked for a memory and CPU usage by the 2. To do so I made 2 CONSOLE application (one PHP and one C#)
Both runs on the same machine on linux.
As you see it's the same code.
Memory usage for C#: 88820 kB
Memory usage for PHP: 187872 kB
CPU usage for C#: 0m0.237s
CPU usage for PHP: 0m13.007s
Now the memory usage is... biased as PHP MUST load all the libraries in memory even if not used where C# loads what it needs beside the main VM.
On the CPU side... well it's without comments...