Welcome.
You should get at least 370 KH/s (MH/s) with overclocked 5870.
- Use MSI Afterburner to overclock it.
- Watch your temps (max should be 90°C).
- Lower your mem clock to 300mhz (if you mine bitcoin - not a good idea at this point) and OC your GPU.
- If you get too many stales, lower the clock or increase your voltage on GPU.
If you are trying to mine scrypt coins - OC your Vmem with your GPU.
Thing is my card runs hot. Right now I'm at 750/750 on the clcks getting .03 bitcoin per 24h.
That's about 100bucks US a month equivalent and so it does pay for the internet .

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