I'm just shooting in the dark, but id say a reasonable order size is floating around the $10M level, which is the notional value of the order. This would be equal to 100 lots in say gbp/usd or eur/usd and would equal $1000 per pip.
I've recently seen a documentary, although an old one, where commercial traders will keep firing off $10M trades to prop price up in the market at a given level. If I remember correctly this was a Barclay's trader trading into the London Session, all be it about 30 to 40 years ago!
You must remember though that Liquidity plays a key role in just how significant a order may be in moving price. It's a difficult question to answer, and one that I've always been interested in knowing....How much do you have to trade to move the market, or what would it take
Last edited by Jezzode; 10-22-2012 at 03:23 AM.
You learn more looking for the answer to a question than you do being told the answer straight away.