MSI Afterburner is a great program for overclocking. No reboots, BIOS, or any fancy stuff required.
As for the overclocking, I'd take a decent leap and then test stability for a while. If it works out, try taking baby steps towards upping it some more.
I am running an HD 7870 by Gigabyte and have it running stable at 1175MHz core and 1450MHz memory. That's not to say you will see the same stability and temperatures on the HIS version, although it is by all reports similar in quality to the Gigabyte version.
I would suggest starting out by just increasing the power limit to +20% and going with 1150MHz core and 1350MHz memory. If that works out well, try unlocking the voltage settings in the menu and bumping them to 1300 (assuming the IceQ caps at the same mine does), then trying increasing by 25MHz, one setting at a time, and testing stability / temps again.
Test using FurMark or MSI Kombustor on your native resolution. 2 hours per test is generally recommended, but I've found that about 15 minutes finds your temperature peak and just jumping right into gaming will give you a good idea of stability. If you see graphical anomalies or crashing, you need to clock it back down a bit and try again.
As for the temperature, 85-90c is the peak safey limit, but I'd personally keep it lower than that. My card peaks at 71c on the overclock, which is well within reason.
If you must, set the fan speed on manual via Afterburner and keep it high enough to cool the card down.
Good luck! Well, it's easy, you won't need luck. Have fun!
Oh, and you have good taste in motherboards