Cdc and Gs bring up very valid points i.e. yet should teach us one thing: everything is relative.
Having said that, i think that it is generally accepted that an amp that "doubles down" i.e. produces twice as much power as impedance is cut in half is considered to be "high current" for its' power rating. I would go so far as to say that some amps are "high current" even though they might not "quite" make it to doubling. As Gs stated, obviously an amp that is rated for 300 / 600 is going to produce more total current than an amp rated for 50 / 100, but the ratios of voltage to current amongst the two would probably be quite similar. The biggest advantage to using the larger amp would be that you would have a much greater level of dynamic headroom which in turn would allow one to play louder with less fear of pushing the amp too hard / clipping.
Bare in mind that the above is refering to SS amps as tube amps are a completely different beast when it comes to power output vs impedance. Most tube amps are making use of output transformers and are relatively current limited when compared to a "decent" SS design. In terms of OTL ( Output Transformer-Less ) designs, it would not be out of the ordinary to see an amp that put out less power as the impedance was reduced. This has to do with the output impedance of the tubes / circuitry itself since there is no output transformer acting as an impedance matching device to help the tubes along.
Other than that, there is a LOT more to "good sound" than having high current capabilities. Linearity in terms of THD / IMD, bandwidth, frequency response, transient response, level of bias, etc... are all other specs to take into consideration too. The bottom line though is how the unit sounds to you in your system. I've seen / heard plenty of combo's of "good" gear that simply did not match well together. I'm sure most others here can attest to similar experiences also. Sean
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