Hard drive for Fusion drive: 7200 vs 5400
Fusion Drives store everything on disk, but keep a cache of most used data on flash.

If you are planning on using a lot of different data (like starting, stopping, creating and removing those docker containers and VMs) then the disk part will be used a lot.

I don't know how much the price difference is where you are, but in regards to RAM and disk, I always go for the fastest. I also use lots of VMs and containers and with those big, continually replaced and changing files, I take all the speed I can get.