KH does lag, not very noticeable to be distracting. Game offers the option to install data to reduce load time.IDK about project Diva I've heard that one lags, but in kingdoms hearts I have it as a CSO and I haven't installed the data and it works perfectly. I've always wondered, why does the kingdom hearts birth by sleep tell u to install the data?
With Project Diva, the lag can throw off your timing and cause you to miss a note.