How bout this heigh chart?
http://fineart.sk/show.php?w=898
I dunno about the rest of you guys, but I just found that to be really useful and saved it myself on my reference folder. Thanks Fizz.
Now onto the topic:
If you're striving for a more realistic look then yes, you should elongate the body to make him ~7 heads tall. If you don't mind your guy looking somewhat 'chibi' then you can just leave it as is.
What is looking off in your drawings for me is that the knee is too low in the leg, and both his thighs and ankles are way too thick. Also, his chest and abs, although really defined by the outline, have no depth at all. from the 6pack outline you gave him, I assume you want your guy to look fit. If that's the case you should protrude the chest forward from his torso to give it shape, and you should also make his belly go in a bit at the height of his bellybutton. This will help define his torso more. Also, from the way you drew his speedo, it looks like there is no space between his legs at all. If you feel you need an edit for reference, say the word and I'll give it a shot.