Hello Ian
if you have the funds go for the Fredericksen might add £1k to the sail cost, after all "Its for the Boat " isnt it /forums/images/graemlins/grin.gif
On my previous boat I had a FB main with cars that ran in the tracks with intermediate slugs, and a stack pack main. Superb system, the main and hardware was by Parker and Kay. I believe most of the major suppliers.. Fredericksen etc supply the cars. It saves weight to have them in the luff groove rather than having a new track fitted. Mind you there are some who think it isn't seaworthy as one can only hoist and lower the main head to wind.