[size=12]The left-hand picture isn't quite so clear, but from what I can see, the first two skillets are identical to each other. Both would be slant ERIE skillets, called such since the word "Griswold" inside the round cross-and-circle logo is written with slanted lettering. If they said "Erie, PA, USA" instead of just "ERIE," then they'd be slant EPU skillets. Slant ERIE skillets are dated to 1906-1912 or thereabouts. But I've seen different styles of handle on slant ERIE #9 pans -- one style that's sort of flattened like the other sizes that usually have that logo style, and one style that isn't flattened and looks more like the handles on the pans from the 30's and 40's. It gives me the sneaking suspicion that they made some later castings with that style logo for some reason. I can't tell from your photos which style of handle you're looking at here. Numbers on top of the handle were a later addition, yes. In both cases, the 710 is the part number or pattern number, which had to do with organizing the casting patterns at the foundry. By the way, Smith and Wafford's blue book (The Book of Griswold & Wagner) is the best place to look for this sort of info.
I have a Victor #9 identical to the one that you've shown on the right, and mine also has a faint, script-style 723 part number. The casting and the handle style make me guess that it's roughly contemporary to the inset ERIE pans that don't say "Griswold" on them, which would make it 1904-1906 vintage, according to the 5th edition blue book. There was an earlier style of Victor that has a heat ring that is flush with the edges of the pan, just like the earlier ERIE pans, but yours isn't one of those. Frankly, I've never come across any of those, except in pictures. Later Victors had more markings on them; first adding the words "Cast Iron Skillet" and then also adding "The Griswold Manufacturing Co., Erie PA, USA." The last of those would be called a fully marked Victor, and they're probably in the greatest demand, especially in rare sizes.
I would say that none of those three are rare pans, but that Victor might be the toughest to run across again, just because there's a lot of slant ERIE 9's out there... I'd lose interest after $40 for any of the three, myself. And, of course, I'd want to be able to inspect them in person for cracks and warps, etc, if I were actually involved in a purchase.[/size]