I usually like to wait 3 days before I make determinations about a tube but all I can say isn that out of the box, this tube was better than the 6900 in terms of gain (it sounds louder than the 6900) . Having said that the amount of microdetail heard with this tube is simply amazing. Sound stage had a huge immersive sound and nothing jumped out as being out of proportion to everything else however there is no doubt in my mind that the top end on this tube is more extended as is the amount of detail in the lower octaves than the 6900
In doing a search of this particular 5687 there are countless brands of 5687 all at a very low price. Apparently these tubes I have are made in France for the French military so they are often priced much higher
This could be a new benchmark. Stay tuned
As I said, I can't believe I posted in a tube rolling thread but this was so impactful for me I felt it worth mentioning