Is that where you want to be with your overclock? That's a pretty good job considering the Ivy Bridge doesn't like voltage added at the higher speeds. I also think that 72 is a good temp and to go higher with it would be risky for the long term life of the cpu. A lot of people like and want to achieve a high overclock but they are unaware of the consequences and to go that extra mhz is actually not worth it. So if your at 4.6ghz and wanted to go to 4.8ghz or even 5ghz the performance gain would not be worth the shortening of the life of the cpu. To get to 4.6ghz you have already achieved to biggest performance increase when compared to the stock.
There is always the possability that you have a good overclocker cpu and you could take it to 5ghz without going over 1.38v and if you could do that and be 100% stable with the heat maxing out at 80c then that might be worth shooting for. But if you read the article that I had linked you saw the trouble with adding voltage at the higher overclocks.
Good luck to your efforts.