I think for such an integral part of the bike splurging a bit isn't so bad, plus $35 bucks isn't too bad to wing or save up for. The main reason why I went with the 70 is because the jump to the 90 is so much larger in terms of price without a whole lot of benefit to be had. If nothing else I'd go with the 50 since it's the middle of the road and a nice jump from the 30, but I think you'll be happy with anything that isn't Suntour.