I'd say Goku was roughly Supersonic prior to his fight with Frieza, then when he fought Frieza he became light speed then exceeded light speed indefinitely after that.
It got to a point to where even Gods (kais) couldn't sense his energy level yet looking after the entire galaxy for millions of some years. Lol.
In a V-Jump article, it states that Namek is the same size as Earth, or maybe more.
Goku can travel half the distance of Namek in a max of a single second.
This was written by the manga's publisher, Shonen Jump. Thus, it is irrefutable canon.
The radius of Earth is about 12,726.2 km
So if we add the SSJ multipliers.
Base form: 12,756.2km/s^2
At SS1: 637,810km/s^2
At SS2: 1,275,620km/s^2
At SS3: 5,102,480 km/s^2
At SS4: 51,024,800km/s^2
At SSJ4, Goku is about 170x faster than the speed of light.
Goku is superior to gotenks who flew around the world five times where the plantery motion couldn't be observed, which was scaled at mach 31,000 take it from that, ssj3 goku was way above Mach 31,000..
Light speed statements are mainly hyperboles, in the recent movie BOG we saw bills moving At MFTL speed, traveling a distance which seemed many light years in 26 minutes.