mcm, welcome to Glock Talk.
Neither the G27 nor the G26 is a bad choice. I bought both when I tested them when they came out 15 or so years ago.
The lighter recoil of the 9mm G26 is an advantage, and to a lesser extent, so is its one greater round of capacity. I spent the past week carrying one (and shooting a G26 in Subcompact, Master Stock, and Competition at the GSSF match in Salt Lake City), and I'm perfectly comfortable with that neat little gun.
That said, I've spent a lot more time with the G27 over the years when I needed a small auto pistol. Subsonic for subsonic, 1300 fps load for 1300 fps load, the .40 does indeed give you more power. If you've got good control with both and don't have a particular logistical need (as a cop carrying a 9mm service-size Glock would have in choosing a 9mm G26 for backup), you should be fine with the G27 you already have.
If cheaper ammo is a concern, a 9mm conversion unit for your G27 might be the best of both worlds.