The difference in power isn't huge (slightly over 6%) and the higher top speed is sort of irrelevant for anyone in the US unless they take the car to the track. Note, none of the i3's can sustain that high of an output for very long...the computer won't allow it to keep heat in check.
The handling and 'looks' are probably the two biggest differences between the two. Note that the difference between an i3 BEV versus the REx version incurs a weight penalty of over 10%. So, in theory, a plain i3 BEV should have about the same performance as the i3s REx. To get the extra speed, BMW allows the motor to turn faster, which, if you were to use it a lot, would probably decrease its life. The wider tires/wheels and extra body parts makes the i3s even heavier, decreasing the differences in straight-line performance. But, if you want the looks without a performance penalty, the i3s should do it.