I have had similar experiences. I like to use WFT to estimate what Pardo call's his "Walk Forward Efficency", or the ratio of the out of sample WF profits to just optimizing over the entire time period.
A good system should have as high a WFE as posible. Systems with a poor WFE tend to do poorly in live trading. If you have a parm set that works well over a long period of live trading, then you are doing well!
