Is Stratix II a speed upgrade for Arria GX?

I'm designing in an Arria GX device, but am aware it is only available in speed grade 6. In looking for possible options for a faster device, I see that a Stratix II part appears almost identical in terms of architecture and pinouts, but is available in speed grades 5, 4, and 3.

The two parts under consideration are:

Arria GX -- EP1AGX60CF484CN

Stratix II --EP2S60F484C3N

Are there any significant differences between these two parts, other than speed? Is the Stratix II a drop-in replacement for the Arria GX part, other than re-compiling the design, and possible timing changes due to the speed differences?

Thanks.