Is 4ohm that much better?

One thing to also consider is the noise level of the amplifier.  IN GENERAL, the signal to noise ratio of an amplifier will increase as the impedence load increases, meaning less noise and cleaner sound with higher impedence loads.  I run 6 to 8 ohms routinely for my mains and my subs just so the sound stays cleaner.  As stated above, the amplifier will also run cooler and last longer at higher impedence loads.

The only reason audio manufacturers started using lower ohm loads in car sound system loudspeakers is because of the terrible acoustic environment in a moving car and the demand for lower weight and lower cost in OEM components.  Generally, there is so much road and wind noise in a car and the interior acoustics are so bad that a slightly noisy amplifier is acceptable, as the noise will be drowned out or covered up.  The increase in net loudness for a given amplifier size at lower impedence loads is a good trade-off.  It allows manufacturers to use smaller amps to get the same loudness, which lowers the total weight and overall cost.  After market manufacturers have in recent years been involved in a power war, listing larger and larger numbers as a means to sell equipment.  People seem to want big watts having bought in to the line that higher power is better, so advertising peak power at low impedence and high input voltages is a sales tactic way to attract purchasers.