I'm also of the opinion that Ginyu was holding back. Firstly Ginyu stated Goku is even better than he thought, though Goku seemed to be only slightly so, with me and many others placing him at somewhere in the 60k vicinity, like 66k or so. So Ginyu says Goku isn't the only one capable of altering his BP at will and flares an aura while unleashing a blast that surprises Goku. Still, they seem to fight pretty evenly after that and a difference between them is shown only when they fly away and Goku is shown as faster. Then later Ginyu seems to catch on Goku still concealing his true power and says Goku has a ceiling of 85k... seems weird if Ginyu were already at 120k which would make him way stronger than that Goku. Not only this, but this reserves wouldn't be treated by Ginyu as something Goku is hiding to fight Freeza if such amount were already obsolete by Ginyu's 120k... seems weird, these factors work better with Ginyu being above 60k but still some chunk behind the estimated 85k.
Personally:
Goku (initially) : 66,000
Ginyu (initially) : 66,000
Ginyu (powered up) : 75,000
Goku (powered up) : 73,000
Goku (estimated) : 85,000/full power : 90,000
Ginyu : 120,000