Speaking to the Sonic Youth / Beatles discussion, I've always found the bands to be quite comparable. Sonic Youth is to independent music what the Beatles are/were to mainstream pop. Sure, Lee is not a perfect George figure, but he that's partly because he plays a little of the Paul role as well. We all know that Lee brings the "pop" to the Sonic Youth table, but he's also the underutilized, quiet genius, who often writes or performs the most hummable songs in the band's catalog.
Kim's an anomaly of course. She's the "Paul" in some respects and the Yoko in others, but it's not the similarities between band members and their roles that makes Sonic Youth the Beatles of our little world; it's the prolific output, the endless capacity for reinvention, and the iconic quality of the individual members. I think it's absolutely a fitting comparison. Sonic Youth is just a product of a sub-culture of a sub-culture that the Beatles laid the framework for.
Anyway, the Pixies are more analogous to the Beatles in the musical, interpersonal, and archetypal sense. But while the Pixies are, in the long run, derivative of the Beatles (like: hey, what if the Beatles were geeky college rockers from the 80s?), Sonic Youth is, in my opinion, on the same hierarchical plane as the Beatles. Less "influenced by" and more "Twilight Zone version of"
Does that make any sense? Probably not. I'm totally tuned the fuck out and haven't slept in two days.