You might expect a GPU that's power limited wouldn't have much overclocking headroom, if any at all. Yet the GTX 950-2G doesn't disappoint and offers a 200 MHz core clock boost 800MHz effective memory clock increase.
In performance terms this gave an extra 12% performance in 3DMark but this number will vary between applications depending on the power stress the card is under.
If the card is already hitting a power threshold at stock clocks, when overclocked it will not be able to boost much/any higher without encountering the same issue.