In my view the various accounts of giants can be broken down into a few catagories.
Purely Mythical - simply a legend, think Greek Titans
Mistaken Anatomy - Someone finds the fossil leg bone and skull of a mammoth, they come up with the idea for the Cyclops.
Exageration - Often power and size are equated, so stories about powerful men quickly become stories about big powerful men. There may have been a real Hercules, but he wasn't actually nine feet tall.
Excessive Growth through genetic illness - Robert Wadlow 8'11"
Abnormally Large individual amoung normal population - Shaq
Slightly larger population viewed by smaller population - The 5ft Romans encounter the 6'4" Norse.
This covers all the "normal" giants we'd expect to find. I take it from your post that you would want to include a further group.
Reproducing population of excessively large individuals - numerous people exceeding the current height limitations (say, 8ft+).
I take it from your post above, and on the other thread, that there is physical evidence for this last group.