Difference Between trading One Thousand VS One Million Dollars?

Hi,

I have been reading many stories about how people made a certain % from trading forex, but what I would like to ask is:

Can a system that has been proven to make a certain % of profit on a small volume of trading make the same % of profit on a large volume of profit?

Can the system that made 40% (for example) from $1000 trade also make 40% for $1000,000 trade?

What are the various factors that make it different when trading with $1 million vs trading with $1k if any?

If there is a difference, does it mean that all those people who think that a system that worked to make 40% profit from $1000 are actually indulging in a fantasy when they think it will work the same way for $1000,000?

Does that mean that only systems that actually make a certain % claimed from doing millions of dollars in trading can actually work the way it should for high volume trading?

Goldman Sachs run automated trading, some very big hedge funds do, all with good size, so the answer is yes.
In Forex a million dollar trade isn't that big.

Nic is right - liquidity and slippage don't become a realistic constraint until a fair bit larger than that. Trust me on this...