Thanks for the replies. I realize how much variance can come from amp, manufacturer, etc. and so trying it is the only way.
One thing which patterns these responses that helps me is that the KT66 is definitely going to differ a lot from KT-88's. That's the kind of nudge which helps me move ahead to try it.
@trivema My amp will *not* play a 6L6 so I don't know what it sounds like.