I think it would work better for an adult on it's side.
To be very clear, I think taller cages are good, and give us alot more flexibility in giving them options. But for jobiensis at least, I don't think height should come at the expense of floor area. There are ways using shelves, branches, etc. to better utilize the height, which also create visual barriers (which can be useful for multiple monitors in an enclosure), but it is very difficult to make that space work well. I am not very happy with the boxes taller than they are wide that I have used, then again I'm not all that happy with 3' high cages either.
What I suggest...
1) Understand just how big a peachie is as an adult (I can give you some pics (if you want) of adults, I have seen pics of other adults that were substantially larger than mine though)
2) Start with that cage with a very young small pair. I say small meaning 12" or so 18" at the most. I say pair meaning at least two (they will be too small to reliably know the sexes, there is some gamble in this). I also say pair, in that if you are going to keep this species, you owe it to the monitors (not yours the future w.c.s) to at least try to let them breed.
3) After a couple months, you will have a better idea on how to build out the next enclosure, and will be asking better questions on how it should be built. Then build the next enclosure, make it larger than 3x3, 4x6 (build it as high as you want/can) always seemed a nice minimum for a moderate sized pair to me.
4) Do your homework, don't expect anything overnight
5) Have fun, otherwise you will eventually give up, both you and the monitors lose out.
If all this seems too much work, go get a nice c.b. species, I find peachies are very similiar to some gouldii complex types (engaging, bold, agressive feeder). Don't take that as a failure, it's not, if your not up for the long haul, peachies can be a real pain. You can always get some in the future. I do love all my jobiensis dearly, but they can be very frustrating and heartbreaking at times. If you feel this is only a challenge, and peachies really flip your skirt up (hehehehe I stole that from someone), go for it, they need someone to breed them, and they can be wonderful captives.
Good Luck, any more questions, just ask!
--Robert