Make sure to listen to the interview with Rich Esserman for more detail on actually smoking large bore pipes.
http://pipesmagazine.com/blog/radio-talk-show/the-pipes-magazine-radio-show-episode-127/
I've taken some carving burrs and expanded the bowls on a few pipes (a few
Nordings, a few cheap Vauen pipes, and a lots of
Cobs). It can be hard finding large bore pipes at a reasonable price so I think that modifying ordinary pipes to a wide bore can be a much better solution. From what I've seen factory pipes never go under 1/8" wall thickness so I just make sure to keep that as a minimum, but a pipe with the right shape will leave lots of wall at the rim even with a 1" inner bowl diameter.
There's certainly nothing wrong with a Savinelli 320 though, and the quality and design of my Savinelli Trevi 320 is very good (I only have one or two nitpicks). It's just a little short for my taste so that's why I went and took some Churchwardens and bored them out.
1" is the widest I've taken any pipes recently. Honestly I think a 7/8" (22mm) bowl can be better in a lot of circumstances because it burns more evenly, at just over 1" my widest pipes do burn unevenly more often than others. It's a high maintenance smoke. Though now that I'm sitting here thinking about it, having never tried any wider makes me want to give it a shot just for the challenge.
The Sav 320 is a shallow bowl, which I've come to prefer because my mouth is too sensitive for a long smoke. With deep bowls I just fill it up halfway with carbon pellets (available for just a few dollars a pound on Amazon) and that gives me whatever bowl depth I desire. I can't comment too much on extended smoking times.