Great job. You may notice that the sound is very different, although the notes are completely identical.
Theoretical explanation is quite simple. Imagine several units of some material of different sizes. A similar attack force is applied to them. The sound will be different in frequency and something else. This "something" is called "timbre" - the coloring of sound, reported to it by overtones, resonances, ect.
It's the same with strings. After attack, not one frequency is formed, but a whole set of frequencies, at the peak top there will be exactly that frequency that you wanted. Who does not understand about "peak" - google "Gauss distribution." Actually, difference in sound is due to construction features. 7 and 8 strings are thicker than 5 and 6, that is, the oscillations will be different. And, if we can lower the basic note, then we can not affect the oscillations (overtones, resonances). Yes, there is deeper processing of frequency, but this is another topic.
So, let's sum up. Advantages of 8 string guitar:
- Sound is more natural.
- Wider range.
- You look very cool with this.
Advantages of a 6 string guitar with Digitech Whammy:
- Less weight.
- Frequency changes in real time - it's very suitable for experimental music.
- You don't need to have several guitars with different tunings.
What to choose? You decide.