In theory, its not the number of instruments that will cause latency in a midi daisy chain, its the length of cables. Most manufacturers recommend keeping total midi cable length down to 20 feet or less(total length from last instrumant on chain to interface). Its been my experience that you can go a little beyond that, but when you get out there beyond 25 feet, you do get latency(very small, but its there). Get cables that are just long enough to get to the next instrument if possible, its always a good idea to keep all midi cables as short as possible.

DudeManCentral