Depends on your list...
Each EotG could get you 20 skinks/10 saurus/10 dino birds a turn, which may not die and hence you need more for next turn.
Otherwise, its down to how many slann/lord kroaks you take, and how many other spells you expect to cast.
If you take 1 slann and 1 astrolith and dont cast any spells youre looking 11-13 summoning points per turn, so look at the summoning list and look at what youd like to summon... e.g. a priest on turn 1 and a starpriest on turn 2, or save for a bastilidon on turn 2. Etc. Etc.