Hi there.

Basically the Fusion drive is a tiered logical volume in which data is always sent and received from the solid state drive first, and later older data is demoted to the hard drive. In the case of the Fusion drive data only exists in one place. So the only time that the computer is forced to get data from the hard drive is when the solid state drive has been overloaded.

In short, the Fusion drive will be faster compared to a standard HDD when it comes to booting and loading apps, and if you need more speed you can go with it, but if you decide it's more space that you want, then the bigger hard drive will be a better choice.

Hope this helps.

Cheers! Happy