ACR 4.6 is the last 4.x release, as noted by Tom Hogarty in the blog post linked to above.
CS3 / ACR 4.x users will be able to read 5D Mark II flles via the DNG workflow (i.e., use the free DNG Converter). The same is true for CS2 / ACR 3.x users and CS / ACR 2.4 users.