You didn't mention what case you had and what it has for air flow. If you don't have a fan in the side panel , that would be a good place to add one since it would blow directly onto the motherboard and most likely lower the temp of the North and South bridge. Plus it could drop the cpu a couple of degrees.
Your temps are fine. For NB/SB make sure you've got decent airflow on the mobo like inzone mentioned (make sure to keep the dust out of the heatsinks too). Congratulations on getting to 4ghz at only 1.24v, the D0s often need ~1.3v to hit 4ghz.
Your 920 is a 130w proc and it is normal that it runs hotter than a Sandy/Ivy Bridge chip. Considering you've got a 1.33ghz overclock going, 78c is pretty good. Remember that typical use like gaming won't run all four cores at 100% constantly so temps won't be that high during normal use.