I believe that the axle ratio and gearbox changed in the 4/4 in the last 5 years. The more recent ones are nicer to drive. 0-60 is 0.5 secs difference (factory figures). Therefore the main criteria is do you like a relaxed cruise or are you happy to change gear more often since the higher power / torque of the +4 makes for a more relaxing drive.
Also, if you prefer a narrow car, this is easier to find in a pre-loved 4/4 as you are limited to the relatively few +4's ordered in that configuration or the anniversary models - like DaveW's Bumble.
The body width is identical in both in recent years - width changes are the wings and are a function of the wheels chosen.
Drive both and see which you prefer for your style of driving.
