Thanks for the information. I prefer not to think in terms of you get what you pay for. I paid for a netTALK DUO, which of course is cheap, and the call quality is very inconsistent. Rather than accepting mediocre service and accepting what I paid for I chose to move on and bought my OBI. Google Voice is much more consistent. If you let getting what you paid for be your guide then you allow providers to provide inferior service, even if it's free. I've experienced flawless VOIP with a premium provider (Lingo), so I know the potential is there if a provider has the incentive. GV has the incentive of protecting its good name.
On the other hand, I wasn't aware you can send GV call quality feedback, which I did in this case. I ran the VOIP test and my VOIP potential is good. I suspect there is an excellent level, but good seems OK.