I've overclocked a number of different types of miners, there are a few areas you really need to watch when doing so:
1) Chip temps. The obvious one, as you overclock you will see temps go up geometrically as opposed to linearly as you reach the saturation point on the heat sinks. Likewise efficiency will drop like a rock. Don't trust the on board temp sensors, use an IR gun to watch for the hotspots forming on the backs of the boards as well.
2) DC-DC temps: These are just as critical as chip temps. As the high-side FETs overheat they will cause an avalanche effect where the +12 supply will start to cut through to the chips, increasing the current draw. When this happens the FETs will either dead short or the supply will shut down (if it's a good one. Most are not). Dead short will set fire to the FETs, damage the board, and possibly wreck the hashing chips. Happens very quickly
3) PCIe plug: Monitor the temps using an IR gun on the PCIe plugs. As you pull over 250 watts per plug the connectors start to heat up, which increases their resistance which causes more voltage drop which increases the current draw which leads to more heat which... You get the picture. Also if you use cheap power supplies with 18 gauge wire the wire will heat up and the voltage at the miner will drop from 12v down to 10v or less. This will not stop the miner, what it will do is cause the miner to draw more current which causes resistance effects to become more pronounced which causes more heat which... well, that.
I don't have an L3 or L3+ here in the shop, but if someone would like to send me one for review for a week or two I can give you a lot more information and whatever litecoin it mines during that time. Could be helpful, drop me a line.