As far as comparing the Gold Lion to the NOS tubes, I have no idea what the difference would be. Going from KT88's to 6550's would probably be a big change. There are so many factors involved that its almost impossible to guess at something like this. If it was my call to make and I couldn't somehow do a demo, I wouldn't take a chance; espically if the cost is very high. CJ is a great company and if the tubes in your amp are stock, I would trust that the tubes are a good match. They wouldn't pick a tube that didn't sound good.
Now that I think about it, are the KT88's in your amp stock? The reason I ask is that I don't recall CJ ever using the KT88. I'm not up on their current models, though. The CJ amps I have owned in the past either had EL34's or 6550's.
You may want to give The Cable Company a call. They have a huge lending library of cables, accessories and components. I'm not sure if they lend out tubes, as well, but they have a very big selection. I've used them many times in the past and I find them to be very honest and trustworthy. Even if they don't lend tubes, they may be able to give you some useful info.
Now that I think about it, are the KT88's in your amp stock? The reason I ask is that I don't recall CJ ever using the KT88. I'm not up on their current models, though. The CJ amps I have owned in the past either had EL34's or 6550's.
You may want to give The Cable Company a call. They have a huge lending library of cables, accessories and components. I'm not sure if they lend out tubes, as well, but they have a very big selection. I've used them many times in the past and I find them to be very honest and trustworthy. Even if they don't lend tubes, they may be able to give you some useful info.