You can go WAY higher. Imagine overclocking in this instance is like skipping rocks on a pond. Essentially your +40 core and +10 memory is like you took a teeeeny tiny pebble and chucked it a couple inches. You can crank those numbers up way higher.
For the core clock most people can get about +100-150 (if less than that then your card is one of the unlucky ones) but starting at +50 is a safe baseline, and for the memory you can go as high as +1000 if you're lucky, though it's safe to start at +500 as a baseline for memory.
Using these baselines you should test their stability individually using benchmarking tools like furmark or unigine superposition or heaven. For the core clock, increase the overclock by +5 from the baseline I mentioned earlier and keep pushing it higher until you find your card's limit. Same with memory, except with memory you can increment by +25 each time. Memory overclocking though behaves a bit differently compared to core overclocking. Core overclocking will crash your entire system if it's too high and unstable, while a too high memory overclock will simply produce diminishing returns - meaning you'll get less performance since the memory modules will be outputting too many errors than it can correct. So you'll need to find that sweet spot through observation for a memory overclock.
Every card behaves differently since they are all essentially unique down to their atomic level, what overlockers call the "silicon lottery", so find what works for your system and enjoy the FPS boosts. Also don't be afraid about damaging your card, as long as your card isn't throttling at the temperature limit all the time or has a modified VBIOS to allow more voltage, your card should essentially be fine in the long run.
FYI, I have my overclock numbers in my signature below this ted talk of mine.