What is the optimal number of creep tumors per creep route?

I did some testing and found that about 5 is nearly optimal. You have to wait about 1 second for the creep to reach its maximum spread, which seems ok considering you have to macro other stuff.

With 6 there is no waiting, but I think 6 is too much.

Further information:

TLO hotkeys his active creep tumors so he can hit the perfect timing consistently. He also plays a Zerg style that relies on 4 queens. You might want to watch some of his replays.

1 creep tumour and 1 overlord spewing creep works optimally too.

Simply move the overlord to where you want the next creep tumour to be, leaving creep production on, and when the tumour is ready creep is already at the destination.

This does require a lair though.