Answer 1

High performing yes, but not the highest. Hand written assembly by someone who knows what they are doing can outperform a C++ compiler. Compilers are smart, but they often have to make assumptions on how code is going to be used

Answer 2

Assembly is the native language that represents exactly what the CPU (or sometimes the GPU) executes in a human readable form. For most modern desktops it's x86 or x64 Assembly. Hand written just means you write all the assembly yourself with no compilers for higher level languages involved.

Answer 3

#1 Fortran (4ever :D )
#2 plain C
#3 C++
.... optional with inline assembly