It's hard to know if cutting down the number of targets or frequency will impact anything. We've seen all sorts of crazy issues with router firmware - many things you'd never expect or foresee. Any settings change is certainly worth trying to see if you can isolate.

Probably Google is down, right? (Just kidding!). Removing NAT is a good thing to try. We have many customers using Comcast modems without problems, so I can't say for sure what's up here. You could always try PingPlotter to see which hop the problem starts at. Seems weird that one target works great and 2 don't (especially with something as robust as a Google DNS server).

Sorry I don't have more wisdom to add here. We'd be interested in hearing updates as you discover wrinkles / variables.

- Pete