I'm sorry if my English is really bad
I'm using Kaspersky Pure 2.0 (default setting), since 5 months ago, and it doesn't slow down my overall system at all (it is very light to me).
I don't use Emsisoft Anti-Malware 126.96.36.199 to my primary security software, because it doesn't block add banner, and slow down my overall system but Emsisoft Anti-Malware is the best malware scanner, that i ever know. It can scan almost all malware that i know, but can't remove any malware (Kaspersky Pure 2.0 can remove it)...
Kaspersky is really bad to scan files, USB and etc (i test it), but very few in false-positives.
Emsisoft Anti-Malware 188.8.131.52 can detect any malwares (not false-positives) that Kaspersky Pure 2.0 can't detect! (i test it)
I set a2service.exe to manual (I only use Emsisoft Anti-Malware to scan any files, because of the memory and can't block add banner).
look at this image :
Top : Emsisoft Anti-Malware 184.108.40.206
Middle : Kaspersky Pure 2.0
Bottom : COMODO Internet Security 2012
COMODO Internet Security 2012 is the best personal firewall that I've ever used! (i test it)
I'm sorry if I made some mistakes
I just share my opinion...