I was thinking a giant more than likely would outgrow the 125. Ultimately I'll probably finish my upgrades with a 180g. The clown's will need that eventually.. Is a 180 still to small for the giant?
The LFS about an hour away usually has the snakeskins in stock, this made me think of those. Is the 8" or 10" a more accurate adult size?
I think probably, yes. Big gouramis get BIG. Not sure the max size or if it'd be able to turn around comfortably in a standard 180. It'd be fine if your 180 happens to be wide, but then again, it's a tall fish too, so I dunno. I'd say probably not for life.
Also, a giant would definitely eat the smaller inhabitants of your tank. They can be peaceful up to a point where they reputedly (sometimes) become very aggressive. But the smaller fish will easily fit in its mouth.