I find room temperature makes a massive difference to cpu temps with the ninja. Currently with 20 degree room temperature cpu temp is 43, but once the room warms up to around 25 which it normally does, it will go up to 48, and 51 with the fans on low. Thats on an opty 175 1.47v 2.5.
Higher gpu temps means your ninja is doing its job and the case or casefans aren't. Don't bother upgrading the fan on the ninja until you have done something about your case airflow if you can, as a 4 degree increase in gpu temp suggests bad case cooling.