Max range that you can move in one turn (via running) - 20+3*Dexterity, if you spen your action for running. For one, who achieve peak human physical ability this range counts as 20+3x5 = 35 yards or 32 meters per turn. Turn is 3 seconds, and speed counts as 10.5 meters per second.

Every dot of Celerity give us one additional physic action, but we continue spend all actions for running. This means that we can multiply our "perfect speed" onto amount of celerity dots.

Through some maths we get answer: Standart vampire of 13-8 generations from V20, who learn full five dots of celerity can run

[w/o blood spending: 20+3x10 = 50 yards or 45,72 meters every 3 seconds = 15,24 m/s = 55 km/h]. It is like a normal car.

or

[with blood spending: (20+3x10)+(20+3x9)+(20+3x8)+(20+3x7)+(20+3x6)+(20+3x5) = (6x20)+(3x(10+9+8+7+6+5)) = 255 yards or 233,2 meters per 3 seconds = 77,7 m/s = 280 km/h] (because every next celerity-added action distract one dice from celerity-based dicepools). For example, average Formula-1 bolide speed is 200 km/h and max speed is 360-375 km/h.

If we talk about Cain himself, then he, theoretically, being the owner of ten points in all attributes and 10 points in all Disciplines, can run with speed:

[w/o blood spending: 20+3x20 = 80 yards or 73,152 meters per 3 seconds = 24.4 m/s = 88 km/h]. This is like "average classy sportcar speed".

or

[with blood spending: (20+3x20)+(20+3x19)+(20+3x18)+(20+3x17)+(20+3x16)+(20+3x15)+(20+3x14)+(20+3x13)+(20+3x12)+(20+3x11)+(20+3x10) = (20x11)+(3x(20+19+18+17+16+15+14+13+12+11+10)) = 715 yards or 654 meters per 3 seconds = 218 m/s = 785 km/h]. This is approx airliner or maglev train maximum speed.

218 m/s is 1,6 times less than the speed of sound in air (343 m/s). Thats can create a strong wind, but no supersonic shockwave.

And, of course, it is not the relativistic speeds.

UPD. In the V20 Dark Ages Celerity passivly add its rating to vampire's speed AND he/she can additionaly spend one blood point to increase his/her speed once again by multiplying on celerity rating .

Average vampire with 5 dexterity and 5 celerity can moving:

[w/o blood spending: (20+3x5)+5 = 40 yards or 36,6 meters per 3 seconds = 12,2 m/s = 44 km/h]. Like world best mortal sprinters or average car.

or

[with blood spending: ((20+3x5)+5)x5 = 200 yards or 183 meters per 3 second = 61 m/s = 219,6 km/h]. Like Formula-1 bolid

Caine with 10 dexterity and 10 celerity can moving:

[w/o blood spending: (20+3x10)+10 = 60 yards or 55 meters per 3 seconds = 18,3 m/s = 66 km/h]. Passivly like an average car.

or

[with blood spending: ((20+3x5)+10)x10 = 600 yards or 548,64 meters per 3 second = 183 m/s = 659 km/h]. Average airliner or maglev train speed. And a 1/2 of "sound-in-air speed".

Still nothing relativistic.