I drove both when purchasing my previous IS,it may just have been the individual examples of cars but the manual seemed quite "notchy" through the gearbox,with quite a bit of pressue needed into 3rd gear.
My latest addition has a 5 speed auto,which when driven hard doesnt miss a beat,with no loss of acceleration during shifts.
These cars have been the only vehicles to persuade me not to own a manual,and sure,there are times where I wish I could reminisce about the GTR skyline of old but owning an auto IS does not make me feel un-inspired to treat this as a true drivers car,as it certainly does perform like one!