Stealing a safe is a whole other class of crime from just breaking into a house, it's a federal felony with big sentence attached. Anyone knowledgable enough to cut a safe out of concrete or crack it would know that and wouldn't risk it over a few guns.
A torch wouldn't do it in a reasonable timeframe, a plasma cutter would, but that's a pretty bad idea on a safe with 20-30 lb. of powder inside(hang a sign or pick up the pieces after, your call.)
Now, that being said my safe weighed 700lb. empty when I picked it up, and I got it off the truck and into place in less than 20 minutes by myself with nothing more complicated than a good dolly and a prybar, BOLT IT IN, in concrete, preferably through the floor AND wall, preferably in a corner or a place where there's no direct line of pull for a vehicle, and that's pretty much the best that can be done. An alarm and video camera helps too because thieves need time and a good alarm denies it to them.