There is no performance difference between the QODBC Server Edition license and QODBC Read/Write license.

There is no difference in the commands, queries, data, or schema between the QODBC Server Edition license and QODBC Read/Write license.

QODBC is a client-side driver that typically resides on the workstations/client machine(s).

QODBC Server edition license is required when you have any service-based application like SQL Server, Web Server, and Windows Service connecting to QODBC or installing QODBC on a Terminal Service/Remote Desktop Service enabled machine.

QODBC license depends on the application you want to use. When the machine uses the services like a web server, PHP MS SQL Server, windows task scheduler, and connecting to QRemote/QODBC needs a server license.

So If you are using any service-based application, you need QODBC Server Edition.

If you want to use a desktop-based application like MS Access or MS Excel and access Read Only, you need a QODBC Read Only license.

If you want to use a desktop-based application like MS Access or MS Excel and you want to Read Write access, then you need a QODBC Read-Write license.

QODBC licensing is machine-wise. QODBC licensing is machine-wise. You need to buy a license QODBC/QRemote for each workstation you want to use QODBC/QRemote driver(s). If you have a QODBC Server Edition license activated on your Server, your workstations, if using QODBC/QRemote driver(s) directly, will still need a QODBC License.

Also, refer to the following:
QODBC Licensing Information
QODBC with QRemote Licensing Information