What is more important is to find the lowest ohm load the speaker will present.

However, most mainstream speakers present very stable ohm loads and can be driven by any amplifier, regardless of wattage. The best amplifiers will always double their output every time the ohm load is halved, i.e.

An amp that puts out 100 wpch into a 4 ohm load should be able to put out 200 wpch into a 2 ohm load.

Like the Bee said, clipping is noticed as distortion. Your amp runs out of power, and then goes into clipping, which, if not soft, can damage your speakers quickly.

More indicative of the amp you should buy is the stat above the ohm load, which is speaker sensitivity. The higher the number, the easier it will be for your amp to drive them, and the louder they will get with less power. As a rule of thumb, anything 92 or above is pretty efficient.

As a contrast, my Martin Logan CLS's can present an ohm load as low as 1-1.5, with a sensitivity of only 86db! To drive these speakers I use 2 sets of monobloc amps:

Tube: VTL Deluxe 120 (60 wpch triode mode, 120 wpch tetrode mode)
Solid-state: Classe CAM 200

Using unbalanced inputs, the VTL's will drive the CLS's to almost the same level as the Classe's. The Classe's add 6db of output when you use the balanced inputs, however.

BTW, a tube amp will always clip more softly than a solid-state amp, making them much less apt to destroy your speakers. (mind you, to drive your speakers to such a level would be ridiculous spl levels)