MAX 10 -I7 or -C7 speed grade and DDR3

The MAX 10 Memory Interface User Guide says the -I6 speed grade is to be used for a DDR3 memory interface, but that device isn't available in Quartus.

As it doesn't explicitly say is not possible to use lower speed -I7 or -C7 devices, I'm wondering if that is possible with, of course, a lower frequency, would appreciate any feedback about this.

Thanks in advance