AMD Crossfire Enabled or Disabled?
Been testing oclhc-plus and oclhc-lite with both Crossfire enabled and disabled on a Win7 x64 with AMD cat 12.8 drivers. The results are below:

oclhc-plus v0.08
Hashes: 1.6 mil

With Crossfire
MD5: 1631.2M
NTLM: 2423.6M

Without Crossfire
MD5: 1651.9M
NTLM: 2432.4M

oclhc-lite v0.11

With Crossfire
MD5: 7560.2M
NTLM: 16082.4M

Without Crossfire
MD5: 10514.0M
NTLM: 18872.3M

With oclhc-lite, the speed difference is spectacular, it's much quicker disabling Crossfire and with the NTLM test, the speed did drop a little more towards about 15670.0M.

With oclhc-plus, I was using 1.6 mil hashes which is a lot and they was hardly any speed difference, just slightly faster with Crossfire disabled. I believe if there were say only a couple 100 hashes the speed difference would be obvious.

Conclusion: If you want speed, disable Crossfire for AMD based GPUs.