It again depends on what time of the day you are placing these orders. The first and last 30 mins, hardly any impact cost. But the rest of the day, it might get little tricky exiting 50 lots as limit if you are very particular about a certain price.
I think the best way to play is to include the impact cost as part of your strategy. So assume that every trade will cause you a 10 point loss entering and exiting, place a limit order higher by 10 points for buying, and lower by 10 points for selling and execute as soon as you have made up your mind to enter/exit.
I have seen many higher lot traders getting caught with positions trying to get the best possible price, trying to be penny wise pound foolish.