The size of Sony format ebook fonts depends on the ebook, but ePub ebooks don't usually specify the base font size and so are more consistent.
Sony's windows software initially emulated a PRS-505, but now emulates a PRS-700, see
Sony's Windows ebook Reader. See the attached screenshots from this software, which should be very similar to an ePub on an actual PRS-700. Only the 1st 4 sizes (S,M,L,XL) were available (XXL not available). I think the 1st 3 are the same as the PRS-505, but this should be confirmed by an owner of the device.
Unlike most EInk readers, the Kindle has a built in screenshot capability. So compare the attached to the 6 Kindle
Font Sizes.