I have a relatively short transport pipe run from my MFR tree farm to my base (about 40-50 blocks). I am just using stone transport pipes, and I have at least 1000 items in the pipe at any one time (maybe more since the tree farm is running nearly full speed and harvesting leaves). As it is, it still takes over 2 minutes for items from the farm to make it down to my AE system. I don't have a lot of lag in this system, but I would not want to stretch something like this any further than it is. Even now, I'm contemplating running my AE system all the way there, or moving the tree farm closer.
I have a remote bee area about 150 blocks away, and even for that short distance, I'm going to be using tesseracts for sending items. I wouldn't want to keep all the chunks in-between loaded just for a pipe transport system.