Jim Murphy told me to go with 8'. He says he's seen deer jump 6' fences all the time and he should know. Their garden was eaten down to NUBS before they got deer fencing. He and George Doorakian use the same kind of deer fence, either Benners or Deerfence.com, which they both recommended to me. I've put it off but MUST do something soon!
NONE of the repellants I've used - Milorganite, Deer Scram, Deer Off, Liquid Fence, you name it, they aren't working when the deer decide they love your daylilies. Oh, have used the soap, hair, egg whites, hot chili pepper mixes. None of it works sadly. Wish it did.