Similar question, with a small twist, for my pending setup.
I'm about to pull the trigger on L/R Forte III speakers for my new HT, and trying to figure out what to do for my center. I don't have the screen or room space of the OP (77" OLED TV), but am getting a media center (https://www.birchlane.com/furniture/pdp/belen-tv-stand-for-tvs-up-to-70-grck1897.html?piid=30970361) which has an unusually large center cabinet with more than enough space for a Heresy III to fit in the middle (with doors open, of course).
The Heresy III would also fit in either of those side cabinets, but with only about 1/2 inch of room on the sides and would have to play through that door iron weave. However, this would free up the center space in the cabinet for the A/V receiver and other large items which need room.
My other choice is as noted above, to abort the vertical speaker and go with an RC-64II on the top of the media center. However, more expensive and I'm not sure would sound (and match) better than the Heresy III.
1- Go RC-64II on top. Good - Cabinet space preserved. Bad(?) - Does it sound good enough to hold up to the Forte IIIs, and worth the ~50% increase in price vs Heresy?
2 - Go Heresy III in center cabinet. Good - Should match Fortes quite well, is centered nicely. Bad - Huge space waste for media center, will vibrations or other distortions happen? Is it a problem to have the center speaker that 'low', knowing the Heresy III has a built-in upward toe?
3 - Go Heresy III in either L/R cabinets. Good - As above, plus reclaim the center cabinet space. Bad - Will a slightly off-center center sound weird? It will be close to one of the Fortes (probably 12-18 inches), but I think the Heresy imaging is wide and maybe can tolerate ~2 feet off center axis? Same question on vibrations/distortions.
4 - Go Academy on top. Good - Lots of internet suggestions that it's a good timber/quality match Bad - Won't look as modern as new Fortes, looking at specs still seems to not be as good of a match as a Heresy III, and where do I buy a used one with confidence?
5 - Bag the whole dedicated center thing and use the Fortes as a phantom center. Good - Cheap. Bad(?) - Will a 2 x 4 row seating arrangement (roughly 8 and 12 feet) get reasonable imaging? The Forte III imaging to my ear was amazingly wide, so perhaps.... I realize at least 1 post above strongly advises against this.
Hope this isn't considered a thread hijack. My considerations are close enough to the OP that I thought we could both benefit from common advice.