I used the 6:1 on my H16 and I now use a 7:1 on my TheMightyHobie18. Big difference on the H16 with the 6:1. I would sail for about 8-10 hrs on a good day and my arms were no more fatigued than the rest of my body. On medium to heavy air I would use the ratchet on the main block. If you have it reaved correctly when you sheet in the ratched wheel will spin. When you sheet out the ratchet wheel will not spin (hence the ratchet). Applying a slight force (by pulling) on the main sheet will "lock" it into the block without cleating off. This makes a huge difference after a few hours on the water. Being able to hold the main sheet in your hand so you can sheet out when you need to is great.

Go for the 6:1 set up.