Well, there are a few of us here that have done centuries and club rides on Bike Fridays and Swiftfolders. I know others who really enjoy their Airnimals and Moulton/Pashley bikes.

I have a Bike Friday NWT. So I will discuss it specifically.

The S&S couplers obviously give you an identical ride relative to your full sized bike.

A Bike Friday will give you excellent performance but the ride will be a bit different from a full sized bike. Generally a bit more responsive and harsh with respect to certain road imperfections. Performance-wise, you will have a bit of a weight penalty relative to the super-high-end bikes and the gearing is a bit trickier. Today, most people go with the Capreo hub/cassette that is quite wide relative to most road cassettes. Hence, there are times when one will want gearing with greater granularity to get the perfect gear. Note that you could have Bike Friday or the Harris Cyclery create a custom Capreo cassette with a 9-21 or 9-23 spread instead of a 9-26. That should take care of the granularity issue I just mentioned.

A Bike Friday will pack/unpack in about 1/2 the amount of time of an S&S coupled bike. Folding the bike is great during travel. Folding allows my wife an I to rent a regular car without any rack to transport the bikes. If I remove the front wheel, I can fit both of our Bike Fridays in the trunk of our Toyota Echo. Cabs are much less of a hassle with the folding bike ... a nice perk if you break down/cramp/etc., somewhere along your trip.

If you doubt that folding the bike is in your future, you might want to consider the travel seat mast instead of the folding mast. Otherwise I would stick with the folding mast.

Your weight will not be an issue with the Bike Friday. Although it will prevent you from getting a Pocket Rocket Pro/Pocket Crusoe.