If you're serious about cutting your forex trading costs, the advertised spread is only half the story. What actually determines your profitability is the all-in cost — raw ECN spread plus commission — and that number varies significantly between brokers, even ones that market themselves as "low spread." To find the best low spread forex brokers, we built a proprietary spread monitoring system that runs across multiple live accounts simultaneously — not demo accounts, which routinely show tighter spreads than…