50 range, 43 prayer is a decent baseline for a fire cape @people mentioning 70 range, as long as you know what you're doing and have adequate supplies.
But anyway, it's really up to you. Figure out which kind of pure you think you like best (watching PK vids/streams is a good way to get an idea) and go with that. Personally, I enjoy ranged/2h pures, so that'd be 80+ range with 60 attack and high strength.
Also, a note about prayer - because ultimate strength gives +15% strength, it's the equivalent of having a 15% higher strength level. This means that somewhere in the high 80s for strength, prayer levels become more valuable to pures than strength levels.