I have seen CIS combined with Spybot 1.6 bogging down a powerful i7 laptop. The combination did a serious number on the performance.
From what I see here at the forums Avast is working.
When needed add the installation folder of CPF to the exclusions of the AV program… When the AV also has a sandbox decide which of the two sandboxes to use.
I have Malwarebytes and Super Antispyware Free installed. I also have Hitman Pro, TDSS Killer, gmer and adwcleaner.
I’m using CFW with Qihoo 360 total security and I’m very happy with it.
Qihoo can be used as cloud av only (which is what I do) or you can add bitdefender and avira offline databases. In any case it’s quite lightweight (more than the full CIS)