Barrel Blast only hits for 150. For Cactus, in my opinion the best upgrades to use for her is Popcorn and Bon Voyage.
Unlike Captain Deadbeard, If Cactus has the Popcorn upgrade equipped, she has the ability to deny revives from vanquishing them at a long range if the player trying to revive doesn't see the potato mine and gets vanquished. The potato mine actually has a chance of being armed underneath the downed zombie, so they won't be able to see it and so they walk over to the zombie to revive, and next thing you know it...SPUDOW!
So with that upgrade equipped, she gets more rewarded when vanquishing zombies because on average (let's face it) their hitboxes are smaller, both head and body.
Bon Voyage is useful because if you're being rushed by a Super Brainz, you deploy a temporary potato mine beneath you, and while Super Brainz is focused on hitting ranged attacks at you, and not the ground, he will get vanquished if no overhealth is applied to him. Either way, he is taking massive damage from the explosion if he does have overhealth, so you can finish him off with your close-range attack.