Is differential affects car speed

It is one of the things which does, yes. The higher your rear end ratio, the quicker you can take off, but the higher the RPMs you'll turn at speed, and this can limit your top speed. So, if you have, say, 3.55 rear ends, your tires will make one full rotation for every 3.55 turns of the driveshaft. The higher that number, the higher the number of turns.

Other factors to take into consideration are transmission final drive ratio. Most cars since the late 1980s have overdrive transmissions, meaning that the transmission output shaft turns faster than the input shaft when the vehicle is in Top Gear. There's a ratio to go with that, as well. For example, the 4L60E transmission used in a number of GM cars, SUVs, and light duty pickups has a .69 overdrive ratio, meaning that, when you're in that top gear, the output shaft makes a full rotation for every .69 rotations the input shaft makes. Overdrive can have you turning less RPMs at higher speeds, but it also puts a parasitic drain on the engine.

Then, you factor in tire size, and the corresponding number of revolutions they make with each mile. The larger the tire size, the less revolutions per mile, and the less RPMs you turn at speed.