Hey
I have both the TGN797v3 and the 799MAX. I'm on NBN.
Both routers are fine, but "dumbed down". I'm on the fastest speeds possible. and I DO get 100MB/sec all the time.
I have a mate who has an iprimus supplied modem.
If I were you I would go with the Telstra supplied router, and take your time looking at the cisco or other routers if you so desire.
Setting up another router as the WiFi Access point and using bridged mode isn't that difficult, but I would avoid it unless you really need it.
The WiFi setup is a doddle, even my technologically challenged neighbour had no issue setting hers up for NBN.
If you have specific questions, feel free to ask.