For me WF testing is just taking a strategy and testing it on bite size pieces of history. If you have developed it on all the data then you only have the next future bite size piece of data to forward test it on – but it should cope better because you had more historical data to have developed it on. However if you developed it on a bite size chunk of history then you will be very unlikely to find that it works on the whole of the rest of history so you could be wasting a lot of time. If your strategy has a million indicators and a million variables then it is curve fitted no matter what you developed it on. If you develop it on a five minute time frame then the limited data available in PRT means that you cannot ever test it on say the 2008 market crash and if that happens again next week then all your WF testing has been pointless as it did not include a test such as that.