Try 459-460 RI. On 270X 4Gb it gives best speed.
What's RI where do I set that?
Go to the Devices tab > choose the Cryptonight algorithm and you will see them. Check my post, that's up a bit, the 2nd imgur link

.
Ah you mean Raw Intensity? I'm new to this software

but anyway if I set that over 128 I get not enough memory error.