Elders, Right now I am with IB and have been trading relatively small 1-3 mm size with them. Never had a problem in fills, slippage etc., no complaints at all. Looking to trade majors EUR/GBP/JPY/CHF and build position size of 20-50 mm, primarily during Tokyo, London and NY open times. Looking to build the 20-50mm position pretty quickly like in <5 seconds. If possible, will like to stay with IB and do not want to move to EBS/reuters right now, at least for next 6-12 months. The reason is too occupied right now with other more pressing matters. I will be ok with execution upto 1-2-3 pip away from best bid/ask. I see liquidity in IB on majors is typically 20-40mm up to 3 pip from best bid/ask. So, theoretically I can just go and hit and will get filled for 30mm in 5-6 trades(since IB restricts trade size to 4-5 mm per trade). My question is what will happen if I show this behavior everyday? I understand that in the interbank space, 30-40mm does not move EUR/USD market more than a pip at most. But what will happen on IB platform. After this behavior for 20 days, will liquidity providers take out liquidity and widen spread as soon as I hit 10-15 mm? Will I be forced to move to EBS/Reuters within 1-2 months? For e.g. if Citi goes and always buys/sells 500mm EUR at London open, then other banks(like GS/DB) know this pattern, but they can just guess if Citi is going to buy or sell on a given day and they will quote spreads based on what they think Citi will do. Citi will not give other banks a chance to re-quote mostly, because they will simultaneously hit 10 banks for 50mm each, thus covering their 500mm transaction in one go. Now, in my case also, banks won't know what I will do on a particular day, buy or sell. But since I can buy only in 5mm increment with IB, it will take me 3 hits to buy 15 mm, I will be showing my cards w/o completing the transaction. Based on my prior behavior, banks will know I will likely buy upto 30mm more, and algos will promptly move their quotes on IB away from me. Net result: I end up buying 4-6-10 pips higher than normal market! (who knows how much higher!) Maybe, my reasoning is nonsense, and doing 20-50mm with IB quickly is not an issue. Anyone doing size with IB, please guide. If you suggest I have to move, where should I move? EBS/Reuters or vcap CAX or somewhere else? Thanks a lot!