I moved from IB to Transact, partially out of the threat of being classified as a low execution ratio client. But, for other reasons as well, such as much lower margin costs, and higher reliability.
I regularly preload limit orders outside the market on the exchange. These are all managed economically, moving themselves only minimal amounts to keep themselves outside the active market, in a range about 10+ ticks outside or so. They certainly do not have to reposition themselves each time the market wiggles. Each is managed by a smart thread by the software.
Often there are limits on both sides of the market, as I may not know in what direction I need to strike. Semi-automatic algorithms are evaluating the situation from both sides of the market.
However, these "resting" limits outside the market, can involve considerable numbers of price changes, until such time as my algorithms decide it's time to strike, depending upon how much the market decides to move up and down.
At that time, instead of submitting a fresh order, the existing limit order(s) are used to strike by moving them to the desired strike price. This theoretically avoids overhead of margin checking and results in a faster strike times.
I look at round-trip times in the range of 60-80 msecs as OK response times. Of course, the limit has probably already been filled when I get the ACK that the price modification took place and, immediately after that, usually (unless I'm "best" in a wide spread) I get the ACK that the order is filled.
I sympathize with those of you who are feeling vulnerable simply because you want to modify some orders in the normal course of trading.
My work is in Futures scalping only, usually on Globex.