Finally got the loos gauge on the rig to check things out....in my case I was having vortex shedding that causes a slight vibration at anchor in light winds (shakes the boat at a very low frequency for a second or two at specific angles to the wind). Tried loose rig tension and then tuned for the best sailing I could get (tight tension in my case - buzzards bay winds). 

The uppers are at 15% (I may increase this a bit)
Lower forward are at 15%
Lower aft are at 13%
Rear stay is 17-19%

In 20 knots, beam reach, full sail (135 genoa) std. rig, exceeding hull speed (steady 104% polar performance based on chart-plotter data) - the lower aft was still going too slack so I may increase them a bit (the gauge is supposed to be within 5% accuracy, and I think in my case it was reading low).

I read that you could not over tighten the rear stay with wrenches on the small turnbuckles - and I can confirm this - the wrenches were making a good 'signature' on the turnbuckle. I may loosen these a bit once I get some more time to tune under sail. When I first tuned it without any gauge I thought I was way overdoing it (not so). I didn't want to get out the meter stick and measure stretch as the selden tuning guide shows (the loos gauge stays on while you adjust).  

Anyway, food for thought...