That's right - Rubber Legs is the wrong speed and the bootleg is notably better. I only mentioned Rubber Legs as it was the first (of very, very many) semi official releases of this material, but even RL clearly wasn't sourced from the masters or even low generation copies.
Do the masters still even exist? It seems unlikely considering how many times this material has been recycled from the same copied / digital sources. The Heavy Liquid box, for example, which aimed to collect a massive amount of 1973 material, uses the same old copies as had appeared on numerous cds over the years.
It's clear that Williamson provided Bomp with a large collection of tapes in the mid 1970s - I wonder what happened to these actual tapes? These would probably have been only one generation (perhaps two) down from the masters so these are what we really need to find, if they still exist. If they could be tracked down perhaps then we could have this material more complete and sounding better than we've ever heard it.