Have never found KIS to be resource hog to be honest, but if this is effecting you then don't blame you for not wanting to stick with it. CIS is pretty lightweight, I use it and can safely say am loving the new version... cannot wait for v6. Would not touch Opera to be honest but that's just a matter of opinion. Chrome is not bad, very good against exploits.. and sandboxed process/tabs unlike Firefox even though that's my main browser (die hard fan lol!). Any extensions, if not I suggest...
WOT (Web Of Trust)
ScriptNo
ABP
As the bare essentials...
MBAM + Hitman Pro is better on demand combo, so dump SAS as they're not what they used to be sadly.
If you choose to go with CIS then you get half decent sandbox (will be better once v6 hits with full virtual..). if not then Sanboxie..
Can't think of anything else to add at moment, anything else comes to mind for discussion then will let you know.