General recommendation for optimum performance?

[ElAfalw]

I'm experimenting a bit with Nim and wondering if there are some general 
guidelines for speed.

For example, I compile with
    
    
    c -d:release -d:danger --gc:arc --opt:speed --checks:off --passC:"-O3 -flto 
-m64" --passL:"-flto" -o:example example.nim
    
    Run

Does this look good?

Any other things to pay attention to? Objects vs ref objects, sequences, 
tuples? Specific operations that I should prefer over something else?

Thanks in advance!