Shamans use 3/8 for any fight where their assignement alows them to chainheal. The stat loss is significant but the set bonus is outstanding. Get used to swap out 5/8 T1 maintank healing, 3/8 T2 raidhealing, healpower for short fights, mp5 for trash and long fights all the time. You have an excuse to get prio on those ony bags if you know what you are doing.
Rogues T2 is said to be OP because of the 8/8 but I believe thats mainly due to it having been ridiculously overpowered on feenix (same mangos core). It got adjusted later on and full T2 fell off the table, you would want to get 3/8 for the set bonus asap and for your BiS list iirc there were head if r10 isnt updated by then (better than T2 with the 2 set bonus if you use r10 shoulders > T1), chest, bracers, belt and only pants if you arent r12.
Prot warriors and hunters are the only classes you would see using full T2 afaik.