That would be fine too. It's generic enough.

How does it lay out, or is that not really an issue?

Why not? I think what makes a bigger difference than the dimensions of the tile is the color of the grout. I was just looking at some photos of subway backsplashes this morning and thinking they looked "hard," very rectangular and in your face. I couldn't understand it until I realized they'd used a dark grout which makes each and every tile a focal point. The photos in question were focused on the counters, not the backsplashes, but it was the backsplashes that caught my attention.

Given that this is a flip, I wouldn't spend much more for elongated subs than traditional subs. In terms of "bang for your buck," I think this is a little point that won't affect the general satisfaction of your future buyer.

P.S. We chose 3 x 9 subways for ourselves and like them a lot.

Thank you! It's an L shape configuration. I too prefer whiter grout with white subways.