The wattage and ohms of a speaker are not related; the resistance for speakers is usually 4 or 8 ohms.
The speaker you connect to those terminals needs to be 4 ohms or greater.
The nominal 8 inch speaker impedance can be 4 ohms, 8 ohms or 16 ohms. It depends on the make of the loudspeaker not on the 8 inches.
this is range of 4 ohms resistance in an electrical device. Ohms is a measure of resistance in electrical qualities. Circuits and devices are rated , or measured for there resistance in ohms to meet a designed electrical need. Is this related to a speaker?
Nothing is better.
If wired in parallel then 4 ohms.
Ohms is a measure of resistance. When the electricity passes into the speaker, some of it is 'resisted.' The ohms rating of the speaker is how much is resisted, and an indication of how much energy it takes to drive it - the higher the ohms rating, the more difficult it is to drive.
The speaker will be fine and there will be little impact on its performance. In these situations, if there is a problem, it will be with the amp because that is what delivers the electrical current to the speaker. The situation you want to avoid is having speakers with a lower impedance connected to your amplifier. So you might have had a problem if your surround speakers were 4 ohms. However, as they have a higher impedance than the amp is set for, I wouldn't worry about it.
There is no single standard. Many computer speakers are rated at 8 ohms while others are 16 ohms or higher. My computer subwoofer here is 4 ohms.
Study ohms law to get your head around it.
For an 8 ohm speaker, 8 ohms is perfect. "Good" and "bad" are relative to the application.
There is really no 3 ohms amplifier on the market with an output impedance of three ohms for power matching. You will find there 0.3 ohm or less for voltage bridging. Scroll down to related links and look at "Interconnection of two audio units - Power amplifier and passive loudspeaker".