Let's revisit the 5150II SLO clip. By that clip, yes they both sound nearly identical. Yet, I've played both, and they are VERY VERY different in person than that clip can show. For example, the 5150 is a tighter amp by a good margin straight in. The SLO is an amp that has the clarity to make the 5150 sound smeared at best. The SLO has a 3D bloom to it, that not many other amps have...ime only a Wizard or a good vintage Superlead/Rev C Recto/C+ has. I'm sure there are more amps that bloom like that but my experience are those I mentioned. But the 5150, any of them, they don't have that. The voicing OF COURSE is going to be close since it's common knowledge that the 5150 was the amp that Peavey designed after EVH gave them his SLO and said "make it this!".
For some, these differences I mention are small and don't matter. But, for me and many others these differences end up HUGE in our opinion of an amp, and they can make/break our decision on a purchase. That's why clips just don't tell me much other than a 'general' tonal example, which is cool, but to me it's less than half the story I want to know about an amplifier.