I have decided not to submit photos of my Cereuseses to cactiguide.com for identification as discussed in the comments on this post, because the identification work had already been done for me. I did a search on cactiguide, and encountered this article, which is well worth reading in its own right, but boils down to:
1. You may as well call it a Cereus peruvianus, because
2. the plant in question is probably the result of accidental hybridization while multiple species were cultivated in close proximity, and consequently
3. the plant might contain genes of any of a number of species of Cereus, including C. repandus, C. hildmannianus, or others,
4. all of which are very difficult to distinguish from one another anyway.
So in this sense, if I'm understanding the article correctly, Cereus peruvianus, though not the proper scientific name for any species of cactus, is nevertheless the proper scientific name for plants like what I have, and functions more or less like a cultivar name.
The situation is sort of the reverse of the one for Neoregelia 'Fireball:' Neoregelia 'Fireball' has the form of a cultivar name but is probably actually a species; Cereus peruvianus has the form of a species name but is probably actually a cultivar. So my blog earns its title once again.