Interesting, I've usually only tested preamps w/ condensers.  The other day at the studio I was testing the new TASCAM UH-7000 at a real studio and the engineer picked up a Telefunken M-80 dynamic since it was close at hand.  WOW.  Easy to hear the difference between the TASCAM, Neve clone and real API.  All the preamps sounded good, and the difference between them was so obvious.  Much more so than my usual testing, where any difference is usually microscopic.  The Barefoots might have helped, but I've done condenser tests in the same room.
 
Something to keep in mind the next time anyone wants to hear the difference in a preamp.  Try a SM 57 or something.
 
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Condensers have a built in active stage buffer amp, which is otherwise thought of as an impedance converter. The actual transducer in the condenser mic is buffered from the preamp by the active stage. A dynamic mic "sees" the preamp and reacts to the preamps impedance more directly than a condenser.
 
Good stuff! 

Thanks Mike.  I remember reading somewhere that dynamics benefited the most from a good preamp, but I was stunned by the difference it made.  And that m-80 sounded great through all of them - very detailed.  Like, uh, a good condenser might.
 
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The M80 is a great dynamic! Best snare mic've ever used. Cool on acoustic guitar of all things too!