CBC is a great place... it's a brewery as opposed to a beer bar (but then again so is Boston Beer Works... but Beer works is walking distance).
CBC is a bit of a distance by cab but not much longer than Publick. I THINK Deep Ellum and Bukowski would be a shorter cab ride.
Although... if you want to hit CBC, you could hit Lord Hobo as well which is about a block away. That's a GREAT place. Actually... that might be my final suggestion. Hop in a cab to CBC, spend an hour or two there, and then walk over to Lord Hobo.
... and apologies on Sunset. I despise the place and whenever "beer bars in Boston" comes up, Sunset gets thrown out immediately. Yes, they have a huge beer selection (115 taps or something like that and 350 bottles). The problem is every time I, or anyone in any of the homebrew clubs I know, have gone in there, almost every beer on tap is a diacytil bomb because the lines haven't been cleaned in forever. All of the beers are served in pint glasses at at the exact same temp. Yes, they have a ton of beers, but that doesn't mean a ton of good beers. I see Sunset as a margarita and fajita bar that has decided to push a gimmic of having a million beers as well. Uur club does the occasional pub-crawl through Boston and we hit 6 or 7 bars... Sunset gets skipped every time.
Sorry again... I don't be to be a jerk about it... I just hate that place and would never send someone there.