As faster recommends, an easy and strong backstay adjuster on such a fractional rigged boat will vastly
improve performance ........ and safety.
The 'upwind' benefits are the ability to FLATTEN the mainsail
in both 'light' winds and heavy winds or when you deem that that youre overpowered. You will also have the ability to better control the amount of mainsail draft ... able to add a bit more mainsail draft for punching through waves in the 12-15kt range. Your amount of desired (tolerated) amount of heeling will be better under control. The amount of increased backstay tension resulting in forward mast 'bowing' - results in mainsail flattening
Adjustable backstay tension also will enable you to easily control the leading edge SHAPE of the jib. Any boat will not 'point' to its optimum if its forestay (controlled by backstay tension) is not 'matching' the forestay sag with the amount of 'leading edge curve' that the sailmaker designed into your jib. If the forestay (backstay) tension is too loose the boat will point poorly (even skid off to leeward), it will heel over aggressively and be SLOW when pointing. With the forestay 'overtightened' the jib will tend to 'curl' at the luff and the draft will tend to move forward with the leech sections becoming flatter .... probably the best shape for 'high speed' in FLAT water; but, 'decreased' power to punch through oncoming waves in the higher wind/wave times.
Here's an article I wrote about the interaction between the forestay (backstay) tension and optimizing JIB/GENOA 'shape' ... how you then 'trim' is up to your 'tastes' and abilities, http://www.ftp.tognews.com/GoogleFil...f%20Hollow.pdf
For a frac. rig, or even a masthead, the ability to easily adjust backstay tension is a BIG plus .... as it controls the SHAPE of your foresail !!!!!!!