I recently bought a Nanoray 600 with factory stringing in bg65. To be frank i dont know the exact tension but it is around 19-20lbs...after owning it for a month i feel that these strings are not functioning as good as my NS6000 w BG68Ti at 21 lbs...so i need help on what strings to choose along with the tension...on the racket it says 17-22 .
bg80 is always a safe choice if you don't want to experiment too much and go for a safe good all-around string. the tension is a personal preference, stick with what you're comfortable at.
i havent used them, but there's quite a handful of threads about strings and comparison in this forum.