Ok, I think one of the (probably several) CTD causes is that I had not enabled Sunset Invasion. Seems in some unpredictable bookmark/character choices, something in that mod is used and if it's not enabled it crashes down. Also, I tried the programs that change the exe header to enable more than 2GB of memory and (this is completely subjective, I might just be wrong) I notice a few less CTD of the kind that happen after a good while of playing.