Transfer speeds are limited by the speed of the host interface, the connected USB accessories and the speed of the storage device. The maximum achievable transfer speed will ultimately be limited to the slowest of the elements in the chain.
Note also that due to protocol overheads, the achievable transfer rate will be lower than the theoretical “headline” rate. Likewise, storage devices usually have lower write-speed than read-speed.
Be aware that attempting to transfer directly from your Camera to an external storage device, such as an HDD, may also be heavily influenced by the software App that is performing the copy/transfer. Speaking from experience, the while the native files App is relatively efficient in copying/moving files from an external device to the iPad - or from the iPad to external storage - relative performance is poor when attempting to directly copy/move between connected devices.
Some third-party file manager Apps are considerably more efficient - offering better copy performance. Perhaps consider Stratopherix FileBrowser - Document Manager, or its “pro version” FileBrowser Professional:
https://apps.apple.com/gb/app/filebrowser-document-manager/id364738545
https://apps.apple.com/gb/app/filebrowser-document-manager/id364738545
You might review the extensive online Manual and help files to determine suitability for your needs.
https://www.stratospherix.com/products/filebrowserprofessional/filebrowser-professional-user-guide.php