VK-55, VK-60, VK-75...

All three of these BAT amps show up with fair frequency on A'gon. There's a bit of a price difference, but not an enormous one, between the later E &F revisions of the VK-60; the VK-75 (which was the VK-60's successor); and the VK-55 (lowest powered, fewest tubes, but newest).

Can anyone which comparative experience differentiate between the sounds of these units? Whether the theoretical difference in outputs matters in 'real world' settings (e.g., w/ 89 or 90 db @ 1W speakers)?

Thanks!