DS3R isn't different from those. The P35C DS3 is.
They differ in PCi-E Xx16 slots. I want two to power 4 monitors.
And welcome to OCN.
the P35-DS3P, DS4 and DQ6 all measure 305 x 244mm, and the layout of components on the board is the same.
the P35-DS3R measures 305 x 210mm. the layout of the components (SATA connectors, PCI, PCI-E, mosfets, etc) is different from the three above. it also uses a less advanced bios.
the P35C-DS3R is different still.