For the sake of compatibility I might suggest a 2.75/1.25/2.25 or 2.25/1.25/2.75 as seen on boards like the M65-A and DZ60. Adding a split right shift option could also help (splitting the shift would allow the unused 2.75u key to be used as one of the spacebars, and many keysets already offer a second 2.25u shift for clueboard/fc660 compatibility).