Re: Backstay tension
An adjustable backstay doesn't make the boat sail any faster or point any higher to windward than it would be capable of sailing without a backstay adjuster. The ability of a boat to sail to windward is limited by it's design. If you didn't have an adjuster, you could get out your tools and adjust your rig more taut, and the boat would point as high as it's design permits. What a backstay adjuster does is, it enables you to change the tuning of the rig very quickly, on the fly, from taut to loose, without getting out your tools. The taut setting enables the boat to go as fast and point as high to windward as it's design permits. The loose setting enables it to sail as fast off the wind and in lighter winds as it's design permits.
If a backstay adjuster is over-tensioned, it can damage the boat structurally. As you have seen, in some cases it is also bad to adjust it too loose. The maximum tension recommended for a boat is generally based on the type and size of the boat's shrouds.