I use CoreTemp to keep an eye on my i5-750 temps and when my cabin is warm, I idle around 28-30C with a CoolerMaster Hyper N520 sitting on top. On really cold mornings I've idled as low as 18C-20C. Load temps on warm days went up to 59C... didn't get load temps on the cold morning.
I guess what I'm trying to say is this... it's all about ambient temps.