Actually TFS (Team Four Star) referenced this. "Nappa is worth Five Raditz". Raditz being 1200, Nappa is 5xRaditz. Which is 6000. Goku is 8000. So while Goku would win, it would take a bit of time because of Nappa's size and physical toughness. A baseline Kaioken increases the users abilities by 50% of their current status. 1/2 of 8k is 4k so Goku was bumped to 12k, which is twice as strong as Nappa and used that to drop him while Nappa charged at Krillin and Gohan.
@nishi99: Yeah but it's impossible for him to be 4k if Goku said he would take forever to fight him without Kaioken. And Goku was over 8000, I actually agree with that 7k though.
Chapter: 226 (DBZ 32), P7.4/P8.1-4
Context: after Goku deflects Nappa's mouth blast
Vegeta: “Unbelievable!! To instantly deflect it at that short of a distance!”
Goku: “Phew. If I had taken that one head on, I’d have been in trouble!!”
Nappa: It…It can’t be!!! That was my…my best technique!!! He…He just bounced it off!!”
Goku: “He really is a tough bastard! Even though he should have been hurt a little bit by my Kamehameha!! At this rate this looks like it will take forever...”
this proves Nappa should be atleast around 7,500 if not 8,000.