I know with networks and communication your connection with someone/something else is always based off of the slowest part. Whether that is someone's obsolete hardware bogging down their framerate (hopefully frameskip keeps the other player from seeing this), their fisher price internet slowing down everything, or if they are still using antiquated hardware like a 10/100 router or switch or a max 300bps wifi extender to play on. You could have the best everything, but when you connect to Billy Bob from the swamp, you are limited to what he has.
To be honest, I don't know if connecting to someone who can't maintain a consistent framerate on their machine would lag on your end... but it would make sense that it would not be optimal.
