I have a 27inch 5K iMac that I bought in February. At the time I couldn't wait for a BTO machine as my work machine had died so i needed one off the shelf. I took the one with a 2TB fusion drive. I'm noticing a slow down in the machine now as it is getting fuller and want to do something to upgrade the storage. One option would be to split the fusion drive and use the internal SSD for the OS and applications, then add an external SSD in a Thunderbolt caddy. The other option is to open the machine (I know it will void the remaining warranty) and replace the regular internal hdd with an SSD. If i went down the internal route, does it still require a temp sensor to be added to prevent the fan running at full speed as was the case with the older iMacs? Would it be worth rebuilding fusion so that I just have one large volume rather than having to split how I save files? Any advice and opinion would be appreciated.