48C is not bad. You can get it lower, but can you stand the noise?
If your system is stable don't worry about it.
You could look into running a duct from a fan mounted on the side panel to feed outside air to the cpu directly. I have a 120 mm fan in the side of my case, (no duct) that lowered my cpu temps about 4C if I remember right.
One other trick that I use is to lower the cpu voltage on notch. I use Memtest 86 and let the system run overnight to make sure that there are no errors. Now, if you are overclocking you would not want to do this
The last system I built I found that I could lower it one notch, but not two. This lowered my cpu temps about 2C.