Most efficient alternator RPM

[wmingin]

Hello Wizards!
Does permanent magnet alternator efficiency increase with RPM?
Would an alternator with small magnets turning at high speed be more efficient than
and alternator with large magnets turning at low speed.

Frequency of output is not a concern, ( converting to dc )

Thanks for reading.
B.

 

[anorlunda]

https://goo.gl/images/1roqAE

 

[wmingin]

Thanks Very Much!
B.