Matching amplifier power to speakers question

This may sound like a stupid question, but could someone advise what the optimal range of RMS input powers would be for a set of 100w RMS speakers?

The speakers in question are a pair of Alpine R-S65c 6.5" components and a pair of Alpine R-S65 6.5" coaxials. They're rated at 100w RMS so obviously this would be the ideal input power, but would you get away with for example a 75w RMS per channel amp,  or a 125w RMS per channel amp? 

How far below or above the rated speaker input power would be considered safe and still effective? I'm currently considering the Alpine R-A60F which is rated at 4 x 100w RMS at 4 ohm.

Thanks