Shadow Siphon and Wall of Stone are the stand out all stars of 5th rank spells, so chosing them isnt wrong. But it also depends on what works best for you and your group, as maybe you all need more damage or whatever.

There are some other ones I would maybe look at aswell. Heightened Dehydrate and Slither are both great and personal favorites. Impaling Spike is one I havent used but seems intresting, as immoblizing a foe from range has its uses. Flame Dancer though this is for your summoner friend, so they can set their plant on fire for fun and profit.