AWS EC2 Volume Larger SSD or smaller volume with Provisioned IOPS

Just creating a couple new small volumes for a new SQL server's TempDB files. So I only need 2 20GB volumes but noiticed on pricing that:

• General Purpose (SSD) - 500GB - 1500 / 3000IOPS = $51.70
• Provisioned IOPS (SSD) - 20GB - 1500 IOPS = $110.76

But something is telling me deep down that Provisioned IOPS must surely offer something more such as a guarentee yet general purpose gives you IOPS in the range of 1500 but based on how much strain the rest of the volumes are under? Else what's the point in using the smaller volume with provisioned IOPS?

Regards Liam