Whats "fastest?" & whats "quickest?" are 2 very different questions.
Low gearing will help you get moving in less time.
High gearing will help your top speed after you've got yourself moving.
How much force you can drive into the pedals, the speed & timing of your shift will determine your actual rate of acelleration to speed.
When I lived in Hawaii in the late '90's I had a Trek 6500ZX with rigid forks and 1.75inch road slicks. (That bike has Rockshox Recon & 1.95inch knobbes, and 2x11 XTR now)...Anyway, In Hawaii, it was a standard 3x7 system with a 12-28 freewheel hub. I would draft city busses, delivery trucks all day long on my adventures. I got tired of spinning out so I "upgraded" to a double road crankset & everything went to h-e-double-hockey-sticks. My raw acelleration power was gone & I never managed to keep a good strong cadence with my established/practiced shifting habit.
My point is there is more to it than just top gear.
All my bikes range from about 28.5 gear inches to about 110 Except the Trek mountain bike. It about 15 gear inches to about 89, now & useless for anything over 22-25 mph even when I'm motivated. If you are going to hang with traffic on a 700c road bike...I suppose nowadays, a 52-36 or a 53-39 crankset and an 11 or 12 to 25 or 28 cassette would be smart places to look. Combine that with good high strength/high torque starting technique to overcome that 35-38 inch low gear & be able to push the 125-130 inch top gear.
175mm crank arms would help in the torque department.
Cadence is about how coordinated & practiced you are, but "spinning" 165-170mm cranks is generally regarded as easier...I ran 170mm for a while & felt "bound up." I have a 33 inch inseam, FWIW. I now run 172.5 to 175's where my torque is higher, my power is higher, my cadence is negligably lower. 87 vs 89 rpm. So I suppose it depends a lot on you, your physical dimensions, your abilities (strength profile, masher/spinner) & how the traffic environment behaves.
Practice your shifting & understand how your gears relate to eachother.
Gears being equal, Much the same applies to 26 inch wheeled mountain bikes too, but you'd be a touch slower in the top end but a touch quicker on the take-off due to wheel circumference.
The trick to riding in traffic at the speeds and methods you are intimating is to stay in the draft. That gets hard & it gets dangerous.
Good luck.
Look at his cadence at speed & how long it took him to get there. Tall gears.