On those systems that has less RAM , having Kaspersky has a real impact, so it's better off using "lighter"antiviruses. On those systems that has enough RAM and processor power, then the tests that's been conducted reflects the actual experience, Kaspersky ain't that heavy on modern systems like it is on older ones.
I know this because I have both kind of systems, a 512MB RAM one and another with 8GB RAM.
Qihoo has been tested by @WinXPert since March, think results are only included if the time of "Product not tested" doesn't exceed a certain number each month.
Here's the results I took from the tester's table, which is filled up next to the reports, just for statistics.
As for Comodo, Firewall v10 is tested since this month by @Av Gurus