> strongly typed variables will always be faster than duck typing.
If the types can be deducted, they'll be just as fast. And when not, you fall into a dynamic case. Such as polymorphism in OOP languages, pointers in C, etc.
> Manual memory management will always be faster than garbage collection.
That's a very strong statement. So you're saying it'll always be faster in terms of total used CPU time to use manual memory management vs. garbage collection?
I wouldn't dare to make a strong statement about memory management either way!
If you're talking about shared heap manual memory allocation, like C malloc/free style, that shared part will make sure it won't scale with CPU core count. You'll also need to track lifetimes of your object destruction. What if some other thread followed a pointer into the structure you're about to free and got pre-empted by the operating system? That calls for more thread synchronization, and puts hard limits to your scalability.
I think if CPUs with tens or hundreds of cores become popular, garbage collection might be the only realistic way to avoid object lifetime synchronization bottlenecks.
> Saying the language doesn't matter with regards to the performance is completely inaccurate.
It affects the difficulty of compiling it into a performant form. Dynamic features do make it more difficult, but just look at the progress in dynamic language compilation in recent years.
Who could have guessed for example Javascript could ever be within order of magnitude of C/C++ performance? But now it is there, and the gap is only getting narrower. In my own tests, occasionally I've seen Javascript and Lua JITters generating practically same code as "gcc -O3 -march=native" does!