2 hours ago, nokie said:If you go for the Nauticam housing (600€ more than the Fantasea), you will get the full 200mm on the RX100, but I would argue you can get a macro lense for less. Of course Nauticam is very good quality, so if that is the preference, the RX100 becomes a bit more attractive.
You need a macro lens (or rather a diopter) with either camera, as neither of them can focus closely at longer zoom extension. However, RX100 VII will give you more magnification with the appropriate diopter. Also, Nauticam is not the only option for RX100 VII - SeaFrogs Salted Line ($247) with macro port ($99) will let you use it at full zoom.