The biggest difference in 3 or 4 is the added area of the flex hoses to expand on the -4 sizes----3 always gives a better more solid pedal feel

Dave to answer your PM question---I have bought mostly from tubesales who have a warehouse right near me and I pick it up so shipping isn't an issue

The best price does come from buying several hundred feet at a time as footage equals price savings---also some stuff may have been on there racks for a while and you can get a retroactive price break---find the salesperson for your area and PR him about racing, etc---you can generally talk them into a better deal---generally different sizes can be added together for better per foot prices --brake and fuel line adds to the footage total and can turn into a
purchase into a much better deal

Jerry