I would think Luffy's Gear 4th would combine Gear 2nd and Gear 3rd, but Luffy would pump more blood making his body hotter so he could fight Admiral Aokiji with out being frozen and instead of having one part of his body being that of a giant he would spread it out evenly across his body. It would get rid of the lag for transfering it all to one place since it spread out. The bones would also stay soft but firm at the same time. I think this would open up a whole new range of attacks and I have thought of some that I think would be very effective.

Side thought~ When luffy leaves Gear 3rd he shrinks and loses all his strength and ability to streach. It would mainly be seen as a downside but I had a thought, what if when he is in this chibi form he is free of the Devil fruit's curse and that being unable to swim. During the time he is in this form he was able to swim in water with out drowning...?

I would love to hear your commets on these thoughts and I am curious to your own Ideas...