Re: 7-string scale.
I personally hate shortscale 7 strings.
I have looked into this a lot and I just don't believe 25.5 is enough.
This was confirmed by Ben Crowe of Crimson Guitars UK, who makes a lot of extended range instruments. I asked him if it was possible to make a 25.5" scale 7 string where the low B didn't sharpen noticably in pitch when struck, because on my 7, a "chugga chugga" low B riff actually requires me to detune to the string slightly to counteract the pitch rising at the start of the attack.
He told me that it is, but that you require a decent length of string after the nut and preferably at the bridge too, that can compensate for the stretch. He recommended a reversed headstock.
Obviously, on a locking bridge, thats impossible, since the other side of the nut is decoupled from the vibrating string.
As such, I personally will now never be buying a 25.5 scale 7 string.