Our experience is that hosting the call takes a lot more processing power and bandwidth than just being on the call.
I have no idea why that would be.

I've not noticed any real workload from hosting a call. I did some testing with Wayne the other day and even with 3 others on the call, I didn't notice any appreciable load on the system.

Our group uses ventrilo and maptools. Vent is better I find for more people. You can also turn off push to talk and make it voice activated (which is what we do).

We use skype for some players. When it is the only major application running on the computer it is fine, anything else running causes problems.

I now have a skype dedicated laptop so I can use a laptop while GMing. We use a video camera pointed at the table for the skype people as we still have most at the actual table.

Vent is fine if hosted, call quality can be adjusted by each vent client. So is more adjustable, but the need of a video camera made more sense with skype.

I'm suprised that Vent is giving such poor quality. In my experience, it has done quite well. It's not quite as clear as Skype, but is still quite good. Maybe whoever has the server settings just picked a lower quality level with the Codex?