Hi,
RDR is not intended to remove these GI seams for cube maps. This is from the change log:
Two new render settings on the Advanced tab which control the region in which ray traced polygons are fully subdivided. Outside of this region the ray traced polygons are only coarsely subdivided. Previously this region was the frustum seen by the rendered image or crop region, but now you can also choose to have no detail or to have detail everywhere within the camera frustum regardless of crop settings. "Ray detail region padding" can be used to enlarge (or shrink) the region. A value of 0 means no padding. A value of 1 adds a border to each side of the frustum which is equivalent to the width or height of the image or crop region, which makes the frustum 3 times as wide and 3 times as tall.
It could help for multiple images taken in the same direction and stitched together sideways to make a long pano ( or for when you're stitching crops together ), but not for a cube map where the images are at such dramatic angles to each other. I'm not sure it's practical to calculate a stable GI solution for a complete location so you can look in all directions and not have issues, but it's not my area of expertise.
My instinct is that you are going to have to avoid using GI for now. I have seen very good results from enviro light setups.
I'll get Matt to check in and make sure I'm not talking nonsense :-).
Regards,
Jo