Magic dmg + is simply adding the listed value to the dmg or what? So a 300 dmg Stone casted with Magic dmg +50 would be 350 dmg?
It appears to add directly to the base V value of the spell, before any int/MAB/weather/affinity/etc calculations.
+99 damage from the club is incredibly potent for the tier 1 spells, pushing them from ~470 (Magian staff) to ~600 per nuke in an optimized gear set (Water becomes 600 damage for 9 MP every 3-4 seconds). The club is only a mild upgrade for tier 2 spells, and a downgrade for any higher tiers. It's also a nice bump for tier 1 -ga spells and -ra spells.
The JSE cape is a very minor upgrade over Goetia, but a downgrade from Taubran, even on the lowest tier spells where the Magic Damage stat is most useful. It is a small m.acc gain over other options, though.
Buremte Hat curbstomps any other head options for nuking, regardless of spell. (Water becomes 700 damage for 9 MP every 3-4 seconds, if paired with the club.)