Ok first of all i hope this match isn't a spite or to much of a speculation but here goes. Wall of tekst incoming....sorry.
This is Slug vs Namek Saga Goku with x3 Kaio-Ken with unlimited time and with no stamina/energy loss but can't go an additional Kaio-Ken.
First of all we all know how the movie timelines are screwed up so bare with me :) The movie witch Lord Slug appears is between episode 81 and 82 Source: http://dragonball.wikia.com/wiki/Dragon_Ball_Z:_Lord_Slug
The PL of Piccolo would be around 1 million and Goku is around 3 million. Looking at the battle between Slug and Goku, Slug was dominating the fight handily against Goku, laughing and mocking him along the way. Slug even lets Goku punch him in the face and it did nothing to Slug showing a huge difference in power!. Now Goku went False SSJ and proceeds to pound Slug. Now even after all those hits Goku landed on Slug even breaking his arm, Slug was still smirking and laughing and was ready for more! and he didn't look as a person who was afraid or was giving up, better yet he transformed and basicly said ok round 2. Look at the battle for yourself and see that after all those hits from a Flase SSJ, Slug still wasn't damaged enough for him to give up and he ripped his own arm off and was willing to go toe to toe with Goku again knowing full well his power and his facial expression also showed his confidence, grining the whole time.
We don't know how strong Goku would have been with the False SSJ boost so thats the speculation that i was talking about but at this pont its fair to say Slug is way stronger than Goku at an PL of 3 million and was tanking hits from Goku when he went False SSJ. So judging the fight between Goku and Slug and False SSJ would Slug stand up against Goku at an PL of 9 million?
I realize the stupidity of the movie because Giant Slug was beaten by Goku by going Kaio-Ken x1 and additional power from Piccolo witch i think is ridiculous because: lets for a moment say that the False SSJ gives an x1 boost similair like the Kaio-Ken so were going at the bare minimum here!, Goku's PL would have been 6 million and althou he smacked Slug around at False SSJ, Slug wasn't exactly giving up like i explained above. Later on when Goku went Kaio-Ken witch would put his PL at...6 million... he suddenly manged to go right trough Slugs's stomach! WTF! i realize that he gained the powers of Piccolo but if thats the case thats only 1 million (if its added that way) witch would make Goku around 8 million BUT Slug is in his Giant Form so his power increased as well so how come Goku suddenly manged to go right trough him? why not before when Slug was even WEAKER.
In the end it took an Spirit Bomb to finish of Slug, even though Goku pierced him Slug still wasn't down and the Spirit Bomb was needed to bring him down. So what do you guys think? would Goku at 9 million be enough or will Goku get beat up? or am i completly wrong about these PL's and looking to deeply into things...would't been the first time :)