Stay 50 attack, get 90 str, and range would be good too. I'd say go for 90 range and 90 str. Range and mage goes great together. stay 50 attack though, g maul wrecks. It's up to you, you could be a pure mage ranger, or even be a g maul rusher, with 50 attack 90 str. Barrage maul, or blitz maul
You could turn it into a zerker. You're 99 mage so you'd already have the level for vengence. You are also very low atk/strength so you could turn it into a range tank. You could also get 75 atk and be one of those SOTD pures, but I'm not sure how well that would work with 43 prayer. Best of luck! Keep us updated and tell us what you do with it!
I think making an initiate/mystic pure would be great, as your mage would support barrage, and you can get 20 defence and switch to dds with the initate. Just my opinion.