Theoretical minimum round-trip-time for a packet to travel over/under the North Atlantic Sea?

Question

I'm doing some performance tuning and capacity planning for a low-latency application and have the following question:

What is the theoretical minimum round-trip time for a packet sent between a host in London and one in New York connected via optical fiber?

Answer 1

I believe the index of refraction of fiber is around 1.5, and the internet reports it's around 5600 km from NY to London, so the theoretical minimum one-way is 5600 km / (c/1.5) =~ 28 ms. Round-trip is double that, 56 ms.

Up to you to do the real work of estimating latency through your routers and all.

P.S. The cables might not be straight :p

Edit: A bit of the wikipedia article on optical fiber pretty much contains all this information.