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How long it would take would depend on the instruction. ARM and x86 instructions should not be compared. The architectures are different enough that comparisons between even similar instructions are nearly impossible to measure.
How much faster is entirely dependant on what you are doing. One task could be tens of times faster, other tasks may only be slightly faster. It depends.
You are comparing apples to oranges. The two processors are completely different and you cannot make a direct comparison between them. CPUs have different cache levels, instruction sets, optimizations, etc.