I thought that the 5150 was a Soldano copy
I don't think the cobra is a copy of anything
I've talked with a amptech, and I told him that my Cobra sounded like MESA Recto / Soldano SLO (not really but something like them), and he said that that's not strange at all. Because Framus Cobra is strong based on the Soldano SLO with a few modifications, but different tubes (el34 instead of 6l6gc).
The dist is identical in Cobra, SLO and Rectifier. (not how it actually sounds but how it's made) If you have much knowledge about how amps are made, you can just look at the circuit schemes. So you call these three amps as a "group" or "family".
The 5150 reminds of these three very much in the beginning, but later in the circuit it's really different. Peavey has copied some of the circuit but not the whole.
I have never tried a SLO but this tech guy says that an original SLO is not as good as the Cobra for metal. Because the SLO hasn't any bass cut/rolloff before the preamp. Cobra hasn't so much either, but it's better at that point.
The more bass you cut before the dist, the tighter it sounds. ENGL is extreme at this point (too tight in my opinion).
That's why so many modify their SLO:s to get better metal sound.
(by the way, ENGL is completely different to these amps, completely other circuit)