A year ago to the day (spooky), This was written...
There is no "perfect ratio"; get the largest amp you can afford / like the sound of.
It's always a compromise, get the best compromise you can. Hypothetically, you may prefer the sound of the lower powered amp to the heavyweight monster, in which case you'll have to be careful with the gain-structure prefacing the amp. In an ideal world, we'd all have something like a Krell "Master Reference" that would have audiophile cred, but with several Kw of oomph; if you can afford it, live in an ideal world (the cheapest way to do this is to build your own amps; you won't save money in terms of power / cost ratio, but you will gain quality if you know what you're doing).
Underrated amps kill exponentially
more driver coils than overrated set-ups.
End of story.