The more serious F18 crews are now running 10:1 mainsheet systems. I suspect the Hobie 20's are limited to 7:1
Pretty much the higher sheet loads are related to the new cut of mainsails, especially the larger squaretops. So there can actually by quite a significantly difference between the modern boats (formula + A-cat + Tornado) and the older designs like H20.
But the Tornado boats are now also using these modern cut mainsails so their required sheet loads will have gone up as well. Unless you decide to use the old classic tornado suit of sails, but these are getting pretty outdated by now. The price for that second hand Tornado will have to be really attractive to serious consider buying it. The new mainsails for a tornado are used since 2001 I believe.
F20's over here use 10:1 and higher as well, I don't know what the US I-20's are using currently. The smallest of the modern formula boats, the F16, is using 7:1 or 8:1 mainsheet systems. A 6:1 system is really too little for the F16's.
Looking at this picture I don't there is any modern boat that uses less then 7:1 for the mainsheet system. But having said this, it is not all about the sheet loads and purchase of the mainsheet systems. It is also about how much the boat needs to be driven with an "active mainsheet". The Tornado is said to be a boat that requires a significant amount of continious adjustment on the mainsheet to make it go or control its attitude. So too the F18's and I don't think the F20/I-20's or F16 are very much better is this respect. The F16 being the least overpowered boat in this series but still a good amount of attentive mainsheet handling is advised here. This tendency comes with the desire to sail a modern boat.
A good mainsheet system goes a long way at allowing your crew to pump the mainsheet for longer periods of fun sailing. The only drawback in going up in purchase is that you'll need longer arms to achieve the same response in the rig. From personal experience I like to limit the purchase system to 7:1 for this reason and my 128 lb female crew is pumping that quite well, so I think we'll stick to that.
I hope this helps.
Wouter
