You have quite a bit of overclocking headroom left.
Intel's max recommended voltage is 1.52 volts, although a lot of us feel 1.40 - 1.45 volts is a safer limit. And 70 C is a safe upper limit for load temps. That is if you want to see how far you can safely push.
On the other hand, there's certainly nothing wrong with 4.4 GHz.