There's an interesting dynamic that science isn't real focused on, at the moment.
Let's say, just for shits and giggles, that the entirety of Antarctica were to melt. All the ice, every last piece of it.
Now, that would take some pretty toasty temperatures, but we're spitballing here, right? So just go with it.
The overall weight of the polar ice pack on the continent itself is enormous. I'd say "incalculable", but I'm certain that some dork has already given it the ol' college try, so there's probably a rough order of magnitude number out there, somewhere.
Take that weight off the continent and you get what amounts to a rebound effect. A certain portion of the continent's bottom end, currently dunked in the mantle by the weight of all that ice, pooches up. This sort of thing is always affects the localized plate structure in a big way, causing various accelerated motions and new rifts - along with the associated seismic and volcanic activity, of course.
The net effect would be greater, overall, than the effect of the sea level rise.