Luffy's G3 attacks are rather slow and quite easy to avoid and Luffy's G4 seems to be somewhat hard to control, with him bouncing around and losing his balance whenever he hit the ground after a big technique. I'm not entirely convinced by this "no trade off". To decide where Luffy is strength wise is extremely relevant to have a perfect understanding of his gears limitations, because otherwise you can be way off with your estimation. There was some discussion regarding that "20 minutes later" thing, i'm not sure if what that referred to was clarified.
Chopper's MP makes him bigger, stronger, much more resilient. I'm not sure if it was said at a single point that it makes him slower, i seem to remember him being more than capable to land attack on some CP9 members pre ts with it. For the most part his speed doesn't really seem to be negatively affected.
It's also interesting to looks at Sanji's DJ introduction, when it was said that the technique is "a leg that gained plenty of heat in addition to attacking speed". So it's basically an addition of elemental damage, and apparently significantly faster attacks, which in return also result in an increase in physical attack power.
G3 is a different matter than G2 and G4 though since it does not work as the latter do, namely an increase of overall attributes, it works more like Diable Jame actually, more power with each attack, so that´s irrelevant.
Second, G4 Luffy has not hsown to have problems to control it, the only limitation we have right now is his Haki usage limitations.
To understand where Luffy is strength-wise, you have to first understand the level of each gear though. In addition, you failed to answer my questions, how would you decide what is more relevant to "figure out Luffy´s overall strength"? It´s not like you can simply combine the twom they each have distinctive fighting levels G4>G2>base Luffy.
It´s simple logic, being bigger makes you slower in pretty much all cases. We have seen that Chopper has pretty good speed with leg point or his new karate point, in Monster Point, he just stands around. And teh fight against CP9 was due to Kumadori shitting himself, and that was only one punch, the second came when Kumadori was barely standing up, which shows the great power Monster Point has really. And being a bigger target has been mentioned several times for big guys.
That translation is wrong though, if oyu have the volume, read it up, it basically says spinning at high speed gives him more attacking power, along those lines, not to forget Sanji has not shown speed gainst with using Diable Jambe.