Okay, i am wanting to know how big of a difference there is between two 7 strings, one of them is a 25.5'' scale and the other is 27'', will there be a huge difference between the two? Will all of the strings be too tight on the 27''? Or will the 7th string be too floppy on the 25.5''? and by the way the tunings i am planning to use are B (regular tuning on a seven string) and drop A (Korn tuning)
The strings shouldn't be floppy on either. String tightness is more due to the string gauge than the scale length. There will be a noticeable difference between the two scale lengths, however. The 25.5" scale means you'll have shorter frets (length-wise, not height-wise). I've heard that longer scale lengths retain intonation better on lower strings, hence why basses have a much longer neck than guitars.
Korn uses straight A, not drop A. I would personally go with the 27.