It would be best to get a Power amp and preamp combination. The watts ratings on the separate power amps are usually more accurate than a receiver. 400-500 Watts should be sufficient. Denon has some good stuff.
Speaker "wattage" is such a moving target and surrounded by such huge amounts of BS as to be almost discounted out-of-hand.
Some basic audio facts:
1. Speaker Efficiency:
Speakers are measured in efficiency: How much sound in decibels will be delivered at a specific distance (usually one meter) at (usually) one (1) watt using a specified type of signal (usually 1000 hz).
So, a highly efficient speaker may deliver in the high-90s in dB at 1 watt at 1 meter.
90 dB is pretty loud, but not outrageously so. However, the increase in sound level is not linear-to-watts-input. To make 100 dB, that speaker will need 10 watts. To make 110 dB, that speaker will need 100 watts. To make 120dB (painfully loud in some frequencies), it will need 1,000 watts.
Each 10 dB in sound level increase is perceived by the listener as twice (2 x) as loud. So, 100 dB is twice as loud as 90, and 110 is twice as loud as 100. But for that 10 dB increase ten times (10 x) the power is required.
What this means is the average loudness of the signal vs. the loudest passages. With highly compressed R&R, heavy metal and so forth, the peak-to-average may be less than 10 dB. What this means is that if you listen to only this kind of music at a typical level of say.... 90 dB, and that takes one (1) watt to make on-average, all you really need is a 10-watt amp (in theory), whatever the capacity of your speakers might be. On the other hand, if you listen to some types of full-orchestra classical music with a P-to-A of as much as 30 dB in a very few cases, you will need a 1,000 watt amp to do it properly. This concept is called "Headroom".
Notice that the minimum capacity of the amp does not change - nor do the speakers care much either - it is the type of music and the intended use volume that determines the wattage required.
Note also that even a fairly poor, limited capacity speaker will _not_ be damaged by a correctly designed, properly functioning high-watt amp at moderate listening levels. I often run a 325 watt RMS amp into speakers "rated" at 100 watts without any fear at all - at the same time I would not intend those speakers to rattle the house next door. And those same speakers while 'rated' at 100 watts are listed as able to accept a 1,000 watt amp (and the associated peaks) for 'most standard musical forms'. But not for a sine-wave, for example.
Cutting to the chase - what sort of music do you listen to?
How loud do you listen?
_MORE_ power is apt to do less damage than less power - it is "Clipping" (another discussion) that damages speakers more so than power - and it is underpowered amps that clip in most cases.
If you like LOUD and you listen to fairly dynamic music (higher peak-to-average), I would suggest you work up from 200 wpc/rms (at 0.10% THD), or more.
Good luck with it.
It's also worth noting that the type of music, the listening environment and the loudspeaker's complex impedance will all play a large role when it comes to the required audio amplifier power required, especially the complex impedance.
The basic rule of thumb is to use an audio amplifier/receiver that is capable of continuous power output that is no less than double the rated continuous power handling capacity of the loudspeaker.
WRT to the terminology used by the author of the lengthier answer: the proper term is speaker SENSITIVITY NOT "efficiency".