Five ounces is considered a typical serving of wine (one glass). So I'd use that as your benchmark. Eight ounces is a bit more generous, but the carb count is still relatively low (about 7g of carbs)... so you can splurge a bit. As long as it doesn't turn into a nightly habit, you'll be fine.
So... go with five ounces as a rule of thumb... eight if you feel you've earned a little more. But no more than eight.