History shows gold has had some great bull mkts. but gold has had extended flat to down cycles as well.  IMO gold will be a poor performer compared to other investments over a 100 year period because there is no income.  We are currently in a bull mkt. & that is the right time to be in gold.

You're missing a key point.  Gold has only been regarded as an investment since 1933.  Prior to that, it was money.  As late as 1971 gold was still money as far as international settlements were concerned.  The "price" until 1933: $20/oz.  Revalued to $35, it remained that way until the US went off the gold standard and we moved to pure fiat.

It makes no sense to talk about money as an investment.  An investment is something you do with money.  So, any comparsion of the investment returns on gold has to start at 1933.   But the correct question to ask is, how does gold @ $20 in 1933 compare to gold @ $900 in 2008?  Has it tracked inflation?  If so, it is performing it's traditional role as money, even if it isn't called that anymore.

There are undoubtably investments that have returned more than gold over that time.  Gold, however, only has to track inflation to live up to it's traditional role as money.

A better way to look at gold is to ask what it buys.  Would a gold coin in 1933 (or 1833, or for that matter 33 BC) buy the same amount of goods and services?   That's the critical requirement gold has to meet to be considered money, ie. retain its value over time.

Personally, I don't buy gold as an investment, I buy it to protect myself against inflation.  As part of my bedrock savings, it's not for sale except in dire emergency.   The reason?  Gold's "value" may fluctuate in terms of fiat currency, but unlike fiat currency, stocks, bonds, and even some forms of real estate, it will never go to zero.