Playing and transferring my records at the correct playback speed is a bit of an obsession for me. A very informative website about this subject is
http://www.normanfield.com/pitch1.htm
I've been using this method for quite some time now, and I found that record speed is pretty much a mixed bag, and even as late as 1932 the correct speed could vary.
But I found some general rules that can serve as a starting point. There are, however, many exceptions to these rules.
76.59 is a good starting point for acoustic Victors. In fact, in many cases this is still too fast. I have many acoustic Victors that play around 75 rpm.
The same goes for early electric Victors. Most of those recorded in 1925 or 1926 play too fast at 78.26 rpm, and should be played at 76.59 rpm or even slower. In 1927 it's about 50-50%, and from 1928 onwards 78.26 is usually correcty.
Many acoustic Brunswicks play around 80 rpm, electric Brunswicks usually play at 78.26 rpm, but there are some exceptions. I have George White's Scandals on Brunswick 105 (recorded in 1932) and I believe it should be played at 77 rpm. And Bing Crosby's "Please" is about right at 76.5 rpm.
Those budget label records (Banner, Perfect, Imperial, etc) were often recorded at 80 rpm. Not always, though.
I hope this helps a little.