iMac 27" upgrade question

[Genericnic]

Hi all.

 

I have an iMac 27" Late 2013 (model 14,2) machine with a 3TB HDD. I'm running the most recent version of OS X Mojave. The performance is dropping and TechTools is giving me SMART warnings that the HDD is not long for this world. Everything else about the machine checks out fine.

 

I have two questions. First, I have never seen a machine in this configuration that has a HDD with a capacity of greater than 3TB. Is is it possible to add a HDD with larger capacity or is it a system limitation at 3TB? This drive will be used primarily for data storage.

 

Second. I am going to add a PCIe blade type memory. It will be used primarily for the OS and applications. Is there any advantage of 2TB vs 1TB?

 

Thanks

 

David