Approx 90 - 105 degrees at a guess. Anything over that and you start to get the image shifting along the horizontal. I was explaining to the Colonel yesterday about doing 360 panos, the bubble type. I would have like to attempted one in there but its carting the kit. Having said that Alderley is one of those where it is worth it.
This is a poor example I did awhile ago before the days of Fenix & WieLED.
http://www.kap.toadstone.com/pdmhs/masson/masson360.html They are not everybody's cup of tea but good ones can give a sense of space or lack of it to someone who has never been down a hole.
Getting back to extending the capabilities of your standard P & S camera. There are a couple of things to remember.
The nearer the subject is to the camera the greater the distortion and therefore limits the pan distance.
When buying software always try to buy the best you can in terms of ability and ease of use. The most expensive ones are not always the best. I use PTgui as well as the original PanoTools on its own, which is the base engine for PTgui.