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.
