Yes but, take this test for example:
http://www.raymond.cc/antivirus/Here is a real life (if you can call it that) test that takes into account several daily tasks and how AV's perform and impact on a given System.
BUT: The test here doesn't specify what types of settings where set for each AV, assuming they are at Default settings -which vary from product to product- hence the given results for each test must be taken with a grain of salt because not all AV's perform exactly the same tasks, they don't all have web shields, network shields, mail shields, etc. Not to mention that some don't even have any settings (Like MSE).
Still, it is clear that Avast! is one -if not the- lightest AV's in the market. I can say for certain that I hardly feel the Suite running on my system, not that I could actually, since my system can easily perform a full system scan while playing HD videos running in economizer mode (that is a speed of 984 Mhz. on the CPU) and not feel the impact.
"So for these tests my guess is that the testers aren't stupid and try to select a scan level which is comparable across the board." I don't dare to affirm that... people are stupid and do stupid things, even testers. I've read tests that testing HIPS software allow Malware to run (disregarding the software's advice) just to see if it is able to stop it later -WTF??-. (this was a funny note, kind of sarcastic even
)
But point taken, Avast! is fast, no doubt about it.
Martin.-