Have found that apparent overkill is necessary if you're using SS. Less overkill is required if you're using tube -- BUT it's advisable to use a detailed, dynamic (fast) tube OR ss.
If you already have the 600's well, why downgrade?
If you don't, then you can get away with less power (BUT not cheap power IMO)... OTOH if the maintenance cost of the 600 is the issue, as you mention, I'm not sure a smaller tube will be THAT cost effective maintenance-wise!
Wouldn't the acquisition cost of the 600's be more of an issue??
If you already have the 600's well, why downgrade?
If you don't, then you can get away with less power (BUT not cheap power IMO)... OTOH if the maintenance cost of the 600 is the issue, as you mention, I'm not sure a smaller tube will be THAT cost effective maintenance-wise!
Wouldn't the acquisition cost of the 600's be more of an issue??