Maybe I'm wrong.
I can't make a proper analysis because my only DSO is a cheap battery powered gadget and combined with an x10 probe it's reading well below the Hameg (which I trust).
<edit> FWIW according to the Hameg the peak to peak voltage into 8R if I pop G string really hard is 130V. That's running at a slow timebase and observing first the top, then the bottom peaks, 264W. I really can't be bothered to get another cab out of storage and see if it hits 112V into 4R for a 400W transient because you wouldn't believe me anyway...