1gpw is pretty efficient and if I was achieving it horizontally.. I wouldn't personally change a thing.
Not even factoring in the time and all it takes to build and "dial" a new room.. Why fix what ain't broken..?
I don't predict you'll have a substantially heavier yield in an amount of time to justify having switched..
But that's what
I personally woulddo. I consider 1gpw the gravy train, and once aboard why not ride it till the wheels fall off.
Then again, vertical may be pushing what's the gravy train standard and if your gut's sayin you can achieve more who am I to kill the vibe...
Edit: Realized I didn't really help at all..
But I'd suggest looking at vert trees.. Low plant counts and the surface area of a 4.5' tall tree by however wide is obviously going to be larger than a flat 4.5x4.5 space. A tree can have 4 sides of that 4.5x4.5' flat space… Now of course that other side or two requires another light to grow..
Efficiency really just comes down to the layout of the space you have, and how you use it… I guess more info or pics of your room would better suit the question? If you have a lot of headspace and some wattage to spare maybe vert trees is actually for you. You obviously have time to veg already doing the scrog thing.