B18C2 standard gearbox = 4.4 final drive
B18C7 standard gearbox = 4.7 final drive + closer gear ratios + LSD

To put it into layman's terms, with a C7 gearbox you will rev quicker (because of the final drive + closer ratios), your car will also be more predictable/pull harder through corners if you plant it (LSD), all at the cost of a little of your top speed.