I've owned a couple King medium bore intermediate tenors lately- a yellow brass 607F that I got here, and I just got a red bell 608F locally. I think these are cool horns and for the price, you get most of a 3B+ with F attachment.
I really liked the 607 and used it for a few gigs, but for the main Disney job it was just a bit too much work so I sold it on. The 608 is in much better shape but hasn't wowed me in the same way- it's a much harder instrument to play and just didn't sound... good. It didn't sound bad but I couldn't get it to blend or center in a section, much less play high or loud on it.
I took it to John Sandhagen today to take the leadpipe out and have a way to use my Edwards .525 leadpipes. It took a bit too much work due to how King put it together....

but it got done. Pulling the original leadpipe, it was pretty obvious why the horn played so strangely and sounded so strange. Below is a picture of the venturi of the two-piece leadpipe- what is shown is the part just after the mouthpiece receiver:

Yes, the venturi on this .525 bore trombone is minuscule. Smaller than a 2B leadpipe. I guess it makes it easier to play for someone, but definitely not me!
With the Edwards leadpipes, it's a completely changed horn. The 1 leadpipe makes it much more 3B like, nice quick front to notes, great high range, smooths out the registers. 2 leadpipe isn't great, not sure why... 3 leadpipe makes the horn wider and louder, not much of a sacrifice in blow either.