the only advantage for the fixed ring....
is that it's cheaper. A track with sliding car will offer you more options to accommodate various sail configurations and is a worthwhile, long term investment for your boat. My C27 has a 5 foot track starting about about 18 inches above the deck, but I fly a racing chute and often raise the pole to eye level. Pole height adjustment is critical when trimming a spinnaker. Clew height determines pole position so if you have more than one headsail or roller reefing you'll want to be able to make those adjustments. On my boat the 140 has a very low clew. The pole barely clears the lifeline, on the 110 it's waist high at the mast.Don't forget that, at the very least, you'll need a topping lift or second jib halyard to support the pole so it won't pull the sail down, a foreguy is very desireable also. 4 feet of basic T track and a simple sliding car with the ring is all you need. No Harken track, it's proprietary, or ball bearing cars are needed in your application. This track: http://www.defender.com/product.jsp?path=-1|118|312064|311656&id=735721and this car: http://www.defender.com/product.jsp?path=-1|118|312064|846725&id=116666will work. Finally, you might get lucky and find the track and/or car at minney's or some other yacht surplus outfit.