IIRC the stiffness increases with width length in Watea series, so 88 would be a bit more ski than the 84.
Another thought, have you looked at the Fischer "Motive" series? I've been very happy with Fischer midfats in various incarnations (Big Stix, T-Stix) and was looking for another last year, but never got a chance to demo Wateas. They were on the short list but I passed for a couple of reasons, the least frivolous of which is that I have a soft snow ski in the mid90's and wanted something more hardpack friendly for my 80's ski. The Motive series seems aimed at this niche, so I looked at those too and ended up with a Fischer Motive 88. It's been this winter's "daily driver" for east coast skiing and if it ever came down to a one-ski quiver (god forbid), this would be it. My only real gripe is that the rockered or early rise tip or whatever they call it flops around a bit at speed but it feels physically stable, it's just a little unnerving at first. The Motive 88 was a 2012 model that I think is no longer in production - but the Motive 86 is out there and I've also seen a Motive 84.