Have you ever seen my A/V-2s?
8x8" top plate, which is why I bought them. They don't offer these anymore.
But the A/V-2s overhang by a few inches front and rear.
The top plate of those you listed is 6 5/8 x 8 - should be OK for large speakers, just need something skid-proof on top. As you can see, mine have screw holes that were supposed to be for spikes, but you could use those to attach a piece of wood to fully support. I've had these stands for years with a number of speakers on them and never had one come off.
My surrounds were also A/V-2s and they were on even smaller plates and they were OK too. I used some drawer liner to keep the speakers from moving.