after spending a few more weeks digging around, it appears that geology is significantly different (beyond superficial changes of HFS) -
1. when aquifers are present they are found in thicker layers, often with a break in between of non aquiferous stone. they seem to be also found in the first cavern layer, leading to some embarks with 'weeping walls' and lag-inducing water flooding. I am still looking for another save with this happening
2. mineral distribution seems more fluid, and / or more common overall. I am no real scientist about this but it seems as though certain kinds of metal-bearing stone can now be found much deeper than before. premium at 900 metal frequency is much more generous with hematite, lignite, bit coal, magnetite than before. and you can find the coal stones in more locations.
now, these changes might just be the results of a fix for a previously-extant bug where iron bearing stone was overwritten, or something like that, during worldgen leading to a serious lack of the stuff where one might expect it. but something has changed, I spent far too long with the 47.05 geology to not feel like something is different here. these stones have changed
gem frequency... cannot say. it does seem a little less than before but, I'm not all that sure. honestly, just generate custom worlds with higher frequency if that's what you want from the game, it's easy enough.