I'm planning to get into forex and have been doing some backtracking and calculations. I see that the current spreads for GBPUSD and EURUSD are 3pips and 2pips, respectively. What is a good a rough average of the slippage that occurs? How wildly does slippage and spread fluctuate depending on the market situation? What's the worst case scenario? Is there a data table out there that lists average slippage and spread fluctuation by week or month? Give me answers in numbers if you can please. Thanks.