Have had a decent amount of seat time in a 991.1 GT3. Even in normal mode I found the pedal progression, balance and shift schedule really well defined and sport mode was a big enough step up from normal. Granted I've never driven a non GT3 991, but too many other hi-perf cars I've driven don't have enough of a differentiation between the modes.
With PDK equipped 911s, the Sport + mode has the most aggressive shift programming, throttle response may be a little more aggressive. Also the 7 speed box will behave more like a shorter geared 6 speed box and never go into 7th gear and hang in lower gears for much longer until red line.
With manual equipped 911s Sport + engages the auto rev match mode when shifting, again throttle is a little more aggressive than regular sport.
On my Turbo, non sport mode is blah and basically for boring freeway cruising or slow traffic, where auto engine start/stop will be activated (can be disable) for stop n go traffic. Sport mode is basically how the car should drive by default, responsive and spirited throttle, more aggressive PDK shift programming than base. Sport + turns the car into a scary monster with very sensitive throttle reponse, super aggressive gear shifting and exhaust will pop and crackle as well.
DSC09400 by Ed Kwon, on Flickr
DSC09402 by Ed Kwon, on Flickr
DSC09399 by Ed Kwon, on Flickr
DSC09394 by Ed Kwon, on Flickr
DSC09389 by Ed Kwon, on Flickr
DSC09414 by Ed Kwon, on Flickr
DSC09423 by Ed Kwon, on Flickr
