It´s not just 7th. it´s the whole gearbox that´s "short"The reason Red Bull didn't have the top speed is not because they don't have the top end speed. It's because Red Bull chose to have a short 7th gear.
They go for acceleration as fast as possible up to their top speed then sit there.
So even though the Ferrari has 10 extra km/h it might not be quicker down the straight because it was out-accelerated from the start up to the RBR´s top speed.