You couldn't damage your card if you tried these days.
GPU Overclocking is a wee bit simpler than CPU overclocking, for starters, there's none of that faffing about in the BIOS.
Start by downloading some overclocking software. There are a few on the market, but the general favourites are MSI Afterburner and ASUS GPUTweak (Generally in that order too). Personally I prefer MSI Afterburner purely because it has an option to apply settings at startup.
Next, download a couple of stability testing programs, I'll list a few:
Unigine Heaven & Valley:
These are very good benchmarks designed to give you some indication of how well your card is performing. At the end of the 2-4 minute run it will give you a score and an average framerate. They both run through 3D worlds created by Unigine and feature a lot of advanced effects in order to really heat things up.
Heaven is slightly older than Valley, but it's also slightly more demanding. Valley is slightly shorter in its run.
3DMark 11:
Try not to confuse this with just the standard 3DMark software, I'll get on to that in a moment. 3DMark 11 has a few tests including one designed to test the physics of the CPU. Again, like most benchmarks, it will give you a score at the end for you to compare - Albeit this one is web-based.
3DMark:
This is a host of various benchmarks, you don't need to run all of them. Generally FireStrike is considered the popular one and it is VERY demanding. Next to Furmark it's perhaps the most demanding GPU bench out there. This too will have a section for CPU physics testing.
Furmark:
The least reliable but certainly one of the most demanding. Furmark is the be all and end all of stability testing - It is purely designed to stress the willies out of your GPU. It cares not for power limits, skipping right over them. Infact I seem to recall reading that both AMD and Nvidia have implemented means of auto-throttling after detecting the running of the Furmark executable. Don't use this program to get a score at the end of it, use it to test that things don't crash immediately - It only lasts one minute if you go for the benchmark option.
You will also need some monitoring software to make sure everything's running as it should be. Afterburner and GPUTweak have quite a lot built in, which is fortunate. But I would also recommend downloading GPU-Z. This will allow you to see real-life non-boost frequencies.
Righty then, overclocking is really quite simple. Start by going up in increments of 20-50Hz on the Engine/Core clock. Keep GPU-Z open beside it so you can see what it results at after hitting 'Apply'. For the moment only work on the core, the memory can wait.
Now here's the tricky bit. GPUTweak lists the eventual boost frequency, so you can up that by quite a bit more: Ie, if the stock says 1203MHz, a clock of 1400-1500 is very achievable. However, Afterburner goes off the actual non-boost clock, so the increments are a lot smaller. As I said, watch GPU-Z for the final clock.
Boost clock and core clock are relative. In theory GPU Boost 2.0 will go up to where it needs to go based on cooling/power allowances. But in reality that isn't such the case. Generally the resulting boost clock will be about 150-200MHz higher than the core clock. For example in my case, a core setting of 1295MHz results in 1447 with boost.
These 970's clock well, especially the memory. The Gigabyte version is perhaps the best. You don't need to worry about temps with these cards, only artifacting. The most I see people get out of them on average is 1.5GHz after boost and 8GHz effective on the memory (I'll come to that in a moment) but you're welcome to play it safe and shoot a little lower.
TDP refers to how many watts the card can draw. 110% or 120% being 10 or 20% more respectively. I would recommend setting this to 110%. The card needs to sip a little more for the OC. These Maxwell chips consume so little that you're not really going to be straining your supply too much to do this.
Memory overclocking works in a similar fashion, it doesn't effect FPS quite as much, but it does help. Fortunately the Samsung memory chips on these cards are just a dream for overclocking.
The kicker here is that effective rates and actual rates differ. In short, multiply the frequency listed in GPU-Z under memory by however many GB's of RAM your card has. In this instance that'll be 4. To offer an example again, I have mine set at 1950MHz, which gives an effective rate of 7800MHz. As I said above, some people have managed to get them up to 8GHz (8000MHz) though I'm not quite brave enough to go that far.
Don't forget not all cards will reach the same. But I'm fairly adamant every 970 could probably reach between 1400-1500 boost on the core - and 7600-8000 on the memory (Effective). Because of this I would recommend bumping your memory straight up to 7600 to save time. Run a bench or two, then bump it up some more in increments of 50 or 100MHz. The memory doesn't have any kind of boost feature to worry about, just that effective offset.
As for voltage - Don't worry about it. Nvidia sets a voltage limit off the manufacturing line depending on how well the chip is binned. In short, this means that they're very conservative. Only on the top-tier cards and aftermarket variants can you sometimes find voltage points on the card itself to bypass such limitations. Basically what this means is that you can notch it up as high as it will go in Afterburner/GPUTweak and the moment you hit 'Apply' it will drop back down to whatever the limit is. Perfectly safe for the card.
Things to watch for:
GPU overclocking is quite straight forward. You overclock as high as you can before noticing any anomalies on your screen. This means either Artifacting (Colour glitches) or worst case scenario - screen going black/machine restarting. You may also reach a driver crash or something if it's too high. Most of the time artifacting is the one to look out for, the rest are quite obvious.
If you're conservative with your OC as I am, you probably won't run in to any of these.
Hope this helps, and have fun out there!
Post any scores from the benches if you feel like it.
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