Hello DougStorms,
Wrong Doug, wrong Bob, I see what you did there
Stretched-cluster is actually likely the best-case scenario for disk-balance if going for a non-homogeneous cluster provided one of the larger capacity hosts is in each site.
If they are both on the same site then this wouldn't be of any benefit here as that added space could not be utilised as each site stores a replica of the others and the lower capacity site would be the limitation - the exception to this would be if you had a significant amount of FTT=0 data which could use that extra space on a single site.
So hopefully there is nothing preventing having one of each higher-capacity nodes at each site.
Bob