Floorplates on the Ren Cen office towers are around 15,000sf - the modern standard is closer to 25,000sf, if not higher. Employers love being able to have their entire staff on a single floor, basically.
15,000sf is not tiny for an office floorplate, but it's not exactly spacious either. And it's on a hexagonal floorplate too, which means there is pretty good access to light. Makes it a decent residential conversion candidate, if not ideal. It's also small enough that it will be challenging to attract large tenants to the building who need more than 15,000sf, as they would likely prefer other options where they would need fewer floors.
Water views also tend to command higher premiums in the residential market than the office market, for what that's worth.
The Hudson's block office component has
ridiculously sized floorplates. Looking at it, it looks like it's around 50,000sf a floor.. It's a desirable office property for that reason.. you can fit probably 3-400 employees to a floor.